“In the depths of his conscience, man detects a law which he does not impose upon himself, but which holds him to obedience. Always summoning him to love good and avoid evil, the voice of conscience when necessary speaks to his heart: do this, shun that. For man has in his heart a law written by God; to obey it is the very dignity of man; according to it he will be judged. Conscience is the most secret core and sanctuary of a man. There he is alone with God, Whose voice echoes in his depths.” VATICAN II, Gaudium et spes §16.52
If one keeps reading the section you quote, they would see this:
In a wonderful manner conscience reveals that law which is fulfilled by love of God and neighbor.(11) In fidelity to conscience, Christians are joined with the rest of men in the search for truth, and for the genuine solution to the numerous problems which arise in the life of individuals from social relationships. Hence the more right conscience holds sway, the more persons and groups turn aside from blind choice and strive to be guided by the objective norms of morality. Conscience frequently errs from invincible ignorance without losing its dignity. The same cannot be said for a man who cares but little for truth and goodness, or for a conscience which by degrees grows practically sightless as a result of habitual sin. -Gaudium et Spes 16
So, ignoring the blindingly obvious paradox of two morally-opposite consciences being equally valid (which other posters have pointed out), we have The Church saying that you must order your conscience properly, lest it grow “sightless”…in the same paragraph which you use to bolster your argument. So, this particular argument is logically invalid.
Catechism, 1782: Man has the right to act in conscience and in freedom so as personally to make moral decisions. He must not be forced to act contrary to his conscience. Nor must he be prevented from acting according to his conscience, especially in religious matters.
Where to even being with this…Probably with CCC 1783 (DIRECTLY following the verse you gave):
Conscience must be informed and moral judgment enlightened. A well-formed conscience is upright and truthful. It formulates its judgments according to reason, in conformity with the true good willed by the wisdom of the Creator. The education of conscience is indispensable for human beings who are subjected to negative influences and tempted by sin to prefer their own judgment and to reject authoritative teachings.
Again, The Church is teaching, as she always has, that in order to follow one’s conscience, it must be well-formed. She also warns against people sinning, by preferring their own judgment and rejection of authoritative teachings. Further on, we see CCC 1786:
Faced with a moral choice, conscience can make either a right judgment in accordance with reason and the divine law or, on the contrary, an erroneous judgment that departs from them.
So The Church is saying here that every decision that one’s conscience makes can either be right or wrong. It never says that, as long as you’re following your conscience, you’re right. Still continuing our reading, we see CCC 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.
Again, people can think they’re conscience is right, and it can still be wrong. If you keep on reading, the Catechism continues talking about rejection of the authority of The Church is a source of evil acts. These acts remain intrinsically evil, regardless of what one believes or wants, and it must be worked at to be corrected.
One of the reasons there are 30k+ Protestant denominations today is because people do exactly what you are doing…picking out portions that suite their beliefs or needs, and ignoring everything else. If you do that, you lose all context. The Church is saying that one must follow their conscience, HOWEVER, one must orient their conscience by using the authoritative teaching of The Church. If you just read the one verse you give and stop there, then it logically follows that the verses I provide prove that The Church contradicts herself (doctrinally speaking)…which would make her not The Catholic Church.
N.B. The magisterium has held opinions which were “ill-suited to their historical context and forgetful of the fact of progressive revelation”. Remember Galileo?
What doctrinally defined “opinions” would you be talking about? It seems you are confusing the infallibility of the Magisterium, in union with the Pope with something it’s not. You would be well served to learn what it really means, because statements like the above betray an ignorance of BASIC Catholic Theology.
HD