Why is Church so seemingly strict? Why can't it change along with the new morality of the rest of society?
(Answers  mainly taken from  talks by Msgr. William Smith  and Fr. John Harvey)

Because the Church follows God's rules by which He made the reality of our spiritual self. God made the physical Universe follow rules such as gravity, force, weight etc., and He also formed the spiritual truths of right, wrong, good and bad. These are unchanging.
Society may exercise its free will to ignore these spiritual rules, but they still exist.
Christ's revealing of what is Truth forms the teaching of the Church.
The Church reminds us that we are not the final authority on what we can and cannot do, but that we owe an account to God of how we act in our lives towards ourselves and others and to Him.This is the way we avoid the danger of the tyranny of rule by the most powerful ruler (eg. Hitler), or the unruly ways of our own passions and desires(amoral anarchy). Animals act by instinct, but we can use self-control for the purpose of good, or give full rein to our desires and demean the dignity in which God created us.
Faith is a form of authority freely accepted, freely submitting intelligence and free will to the direction of Christ - to the Truth given us by God. When we do that, in no way do we become less human.

Speaking in the context of the misuse of the moral development stages of Kohlberg, Fr.John Harvey explains: "To say that you've gone beyond the 'law and order stage' when you go beyond the Church and the teaching of the Church; that you're no longer just a child accepting the teaching of the Church - now you're just a big grownup and you can do what you please - is really a form of self-deception- it's a form of human pride- whereas the acceptance of what God is trying to teach us through the Church is an expression of a fullness of our humanity - we become more free with the help of faith."
 

The first spiritual reality is that there is a God.
God created the Universe - He is God of Life and Truth, whereas Satan is a liar and a murderer from the beginning- a spiritual being who chose not to obey God.
We humans are also spiritual beings who stand in relation to God, and our actions determine our eternal destiny.That is why we have to be concerned with the ethics of our actions.

Our present day society and some quarters of the Church is suffering from a crisis of Truth - from misguidedly being nonjudgmental and tolerating all things, and  by subjectively deciding that "What I want" is right and true for me.

Conscience is the intelligent mental decision (judgement of right and wrong) we make in order to act (what we ought to do or ought not to do). Christian parents help to form their child's conscience when they teach right and wrong.
Listening to the 10 commandments, the teaching of the New Testament and the teaching of the Church is necessary to maintain a good conscience as these are revealed natural and Divine laws and truths.

Our conscience, and so we in our discernment and actions, can be wrong - i.e.. in error ("erroneous" conscience). How does this happen? When you go against your conscience because of desire and temptation, you naturally feel guilty. In order to sin again, you begin to find reasons to justify your actions. Repeated sin kills the conscience's discernment of good and evil.
How are we to be certain that our conscience is correct? If in doubt, we must get more information from an authoritative source, come as close as we can to the Truth of the matter, and the objective and universal Truth must override personal subjective inclinations and opinions. It is the moral underpinning of the Universe and human society. Revealed to us by Jesus in the Bible, it is upheld by the power of the Holy Spirit in the teachings of the Pope and Magisterium of the Catholic Church.

The best summaries of Conscience formation are in the Catechism and in Veritatis Splendour (chapter 2). It was also summarised by the Canadian bishops in their statement on "Conscience" in 1973 . In it they pointed out that
the authentic teaching of the Church is to be preferred to the opinions of theologians.

Catechism of the Catholic Church:
1790. A human being must always obey the certain judgment of his conscience. If he were deliberately to act against it, he would condemn himself. Yet it can happen that moral conscience remains in ignorance and makes erroneous judgments about acts to be performed or already committed.

1791. This ignorance can often be imputed to personal responsibility. This is the case when a man "takes little trouble to find out what is true and good, or when conscience is by degrees almost blinded through the habit of committing sin." In such cases, the person is culpable for the evil he commits.

1792. Ignorance of Christ and his Gospel, bad example given by others, enslavement to one’s passions, assertion of a mistaken notion of autonomy of conscience, rejection of the Church’s authority and her teaching, lack of
conversion and of charity: these can be at the source of errors of judgment in moral conduct.
 

Truth is not subject to a majority vote - (a majority vote crucified Jesus) nor can it be an individual thing "true for me".
Pol Pot after causing the death of 1/4 of his country's population stated that his conscience was clear - conscience can obviously be seen here as being wrong.

"Pastoral solutions" which do not uphold (or which sidestep) the truth by asking the individual merely to "follow your conscience" are not true Shepherding of Christ's flock, which is what "pastoral" means."Pastoral" is not taking the "loving" angle of  false compassion which ignores the laws of the Church. Those that act in true love follow the laws of God because they wish to love Him and do His will.

Law educates us in what society values. Even if lack of enforcement seemingly says the law doesn't really matter when an abortion law is not enforced, a law against abortion is educating society.  Law does have a legitimate function of legislating morality - most laws are based on the Ten Commandments e.g.. stealing is a crime as is perjury and defamation.
The Ten Commandments are God's rules and cannot be changed by men without allowing evil to flourish. Jesus did not abolish the 10 Commandments - remember how He even went further and said that lust in the mind is sin just as lust acted upon is sin?
What Jesus asked was for us to want to obey the Commandments out of love of God, not fear. (Matthew 5:17-30 )
Marriage, the Family unit and respect for life are very important for the stability of society and are worth defending. History has shown great civilizations fall apart from within due to moral laxity.Where each one makes their own rules, anarchy results.

If it is up to the individual to decide their own morality, then why do we know it is wrong to commit adultery? Because even on a natural level, because it hurts the wife and children. Even if it feels good, as forbidden pleasure often does, even if it is emotionally "love", it is still wrong, because of God's laws about marriage. God's wise rules forbidding premarital sex helps teens avoid many emotional and medical problems, while saving their bodies as a temple of the Holy Spirit for the greater joy of faithful married love. Those who give in to their own urges before marriage find it harder to remain faithful in marriage.

"Cafeteria Catholics" have a Swiss cheese conscience - full of holes. We cannot pick and choose when to believe the Church,
because it teaches what Christ teaches.It is a package deal, not a salad bar.

"I'm a Catholic personally opposed to abortion, but I would not impose/vote publicly this way" - is schizophrenic thinking.

Subtle lies lead into error. Fiddling with the terminology is a means of deliberately transforming society - new meanings for acceptable old words e.g.. "tolerance" is the word whereby those with an agenda of licence impose their attitudes on everyone else and are then themsleves intolerant of valid criticism.  In the same way "Inclusive" agenda tend to exclude those who cannot see all things as being uniformly equal because for them some things hold natural priority. "Euthanasia" has changed in dictionaries from "mercy killing" to "treatment for terminal illness"! 

Honest guilt, which alerts a person with a healthy personality that he has done wrong, serves a healthy purpose and dissipates when the wrong has been rectified.  But suppressed guilt, of all the emotions, is the most corrosive to the personality.  If it is repressed, it acts like a powerful psychic acid, eating away at the entire personality.  It will never heal of its own accord.  It must eventually be either resolved or repressed, or the person will ultimately lose his sanity and, ultimately, his soul.
     People can only dispose of guilt in one of two ways:  They can alter their behavior to suit their morality (resolving it the Christian way), or they can alter their morality to suit their behavior (repressing it the secular way).  As Pascal once said, "those who reject God have only two recourses to happiness; to create themselves gods, or to wallow in the pleasures of the senses."
 

It takes courage to stand up for what is right and "preach the truth in season and out of season", but God has a higher hope for us than that we be popular, - He calls us to be holy. In being counter cultural, Catholics are closer to God's reality than to a world run by passions and dubious freedoms. It takes courage to stand up against peer pressure and the easy ways of society, for what is Right and True. But this is our best hope for a peace-filled, just future.
 

Further books and articles on conscience can be found in Catholic libraries:

Pope John Paul 11    Veritatis Splendour Wojtyla, Karol           Fruitful and responsible love  Living the Gospel: a series of statements from the Australian Catholic Bishops Kennedy, John        Conscience and authority  Gallagher, Charles A, SJ       Being the Body of Christ  Sheen, Fulton J    Communism and the conscience of the West  Irish Episcopal Conference     Conscience and morality: a doctrinal statement                            Leclerq, Jacques      Christ and the modern conscience  McNulty, Frank J  Invitation to greatness: how to make a moral decision                                            Dion, Philip E.          Killing a conscience in seven steps  Harrison, Brian   Religious liberty and contraception: did Vatican 11 open the way for a new sexual ethic? Fagiolo, Archbishop Vincenzo   Church can interpret  natural law: "Humanae vitae" 25 years later Zimmerman, Anthony   How proportionalism corrupts moral theology

Quotable quotes:

"Everyone who knows what is the right thing to do and doesn't do it commits a sin."  James 4:17.

"The sin of the century is the loss of the sense of sin." Pope Pius XII

 "If you keep my commandments, you will abide in my love, just as I have kept my Father's commandments and abide in his love" Jesus  (Jn 15:10)

"Indeed, freedom negates and destroys itself, and leads to the destruction of others when it no longer recognises and respects 'its essential link with truth'. Social life is at the mercy of the arbitrary; everything is negotiable, even the first right, the right to life". Fr. Georges Cottier, O.P., L'Osservatore Romano, 25/10/95.

"True law is right reason in agreement with nature; it is of universal application, unchanging and everlasting; it summons to duty
by its commands, and averts from wrongdoing by its prohibitions...It is a sin to try to alter this law...one eternal and
unchangeable law will be valid for all nations and all times, and there will be one master and ruler, that is, God, over us all,
for he is the author of this law, its promulgator and its enforcing judge. Whoever is disobedient is fleeing from himself and
denying his human nature"Cicero (106-43 BC)( in De Republica,De Legbus)

Pope John Paul II in Familiaris Consortio; " ... history is not simply a fixed progression towards what is better,
but rather an event of freedom, and even a struggle between freedoms that are in mutual conflict,
that is according to the well-known expression of St. Augustine, a conflict between two loves:
 The love of God to the point of disregarding self, and the love of self to the point of disregarding God."

"The Ten Commandments are not the laws.  They are THE LAW.  In the final analysis, we do not break the Commandments.  They break us if we disregard them.  How we follow the Commandments will determine whether tomorrow's children will die in bondage or live in liberty."Hollywood film director Cecil B. DeMilleat the New York City opening of his film "The Ten Commandments."
(Quoted in "Can Truth Be Found in Hollywood?"  New Dimensions Magazine, September 1990, page 38.)

Natural moral law "is nothing other than the light of understanding placed in us by God; through it we know what we must do and what we must avoid. God has given us this light or law at creation"
St Thomas Aquinas (Collationes in decem praeceptis, I)

Professor William May says: "The moral teachings of the Magisterium are to be looked upon not as legalistic rules but as precious truths intended to enable the faithful to come to know who they are and what they are to do if they are to be fully the beings God wants them to be: his faithful children, ready to walk worthily in the vocation to which they have been called, ready to follow the call to participate in Christ's redemptive work". Professor William May, An Introduction to Moral Theology, Our Sunday Visitor Publishing Division, Indiana, 1994, p. 244 .

"To have a right to do a thing is not at all the same as to be right in doing it." - G K Chesterton, A Short History of England, Ch.10
"The truth is, of course, that the curtness of the Ten Commandments is an evidence, not of the gloom and narrowness of a religion, but, on the contrary, of its liberality and humanity. It is shorter to state the things forbidden than the things permitted: precisely because most things are permitted, and only a few things are forbidden." - G K Chesterton, Illustrated London News 1-3-20
 "The Ten Commandments do, I think, correspond pretty roughly to the moral code of every religion that is at all sane. These all reverence certain ideas about 'Thou shalt not kill.' They all have a reverence for the commandment which says, 'Thou shalt not covet thy neighbour's goods.' They reverence the idea that you must not covet his house or his ox or his ass. It should be noted, too, that besides forbidding us to covet our neighbour's property, this commandment also implies that every man has a right to own some property." Chesterton, "Do we agree?"1928
"Most modern freedom is at root fear. It is not so much that we are too bold to endure rules; it is rather that we are too timid to endure responsibilities." - G K Chesterton, What's Wrong With the World
"Art, like morality, consists of drawing the line somewhere." -Chesterton,  Illustrated London News, 5/5/28
"Pride consists in a man making his personality the only test, instead of making truth the test. The sceptic feels himself too large to measure life by the largest things; and ends by measuring it by the smallest thing of all." (Chesterton, The Common Man)
 

In an essay entitled, "How Does One Lead a Rational Life in an Irrational Society?" the eminent philosopher Ayn Rand wrote, "One must never fail to pronounce moral judgment. Nothing can corrupt and disintegrate a culture or a man's character as thoroughly as does ... the idea that one must never pass moral judgment on others, that one must be morally tolerant of
anything, that the good consists of never distinguishing good from evil."