Our first obligation is to seek the kingdom of God and His righteousness. 

What would you tell someone in the antebellum South who said their conscience told them blacks weren't people and that it was their right to own slaves?  Would you still say our first obligation is to respect the conscience of others? Why or why not?

The unborn have immortal souls, but so does everyone else.  It doesn't make killing the already born morally justifiable.

So much of this mistaken autonomy of conscience that the CCC speaks of can be boiled down to, "I decide for myself what is good and evil."