At some point, conscience changed from the thing that accuses to the thing that lets you off the hook.
"Conscience" is invoked as an excuse for Catholics who find the Church's teaching on sexuality difficult and don't want to follow it--as if what distinguishes these people is a particularly sensitive conscience. "Celibacy, periodic abstinence, or having tons of kids is OK for the weak, and I really want to stop fornicating/contracepting/buggering my boyfriend like the Church asks, but my conscience just won't allow it!"
Yes, conscience can sometimes tell you to disobey the Church, but that's not what's operating here in 999 out of 1,000 cases. What's actually going on is that following the Church's teaching is hard--sometimes really hard--for a lot of people, and maybe for most people at least at certain periods in their life. So, a lot of folks just aren't going to be able to cut it, possibly for long periods of their lives. Failing to follow the Church's teaching has a lot more to do with "doing whatever you want" and "doing what society tell you is good" than with "following my conscience."
Struggling to live up to the Church's teaching is normal, and we should be understanding, merciful, etc., but there's no need to drag in this false idea of conscience to explain this or motivate our mercy and understanding. Doing so flatters people for being average and removes the possibility of an actual conscience that tells you to do things that are hard.
Moreover, it's an insult to those of us who actually seek to form their consciences according to the Church. Implying that, those who conform themselves to the Church's teaching, going against the grain of society at large, often at great personal sacrifice, do so out of some dullness or lack of moral creativity or inability to think for themselves.
