Another tiny pearl of wisdom from OLiC:
There's a difference between a 'good' conscience and a 'clean' conscience.
If you have a clean conscience, all it means is that you don't feel guilty. It doesn't mean that you didn't do anything wrong, it just means that you don't *feel* badly about it - which could just mean that you've become numb to the wrongs that you've committed.
On the other hand, a good conscience is a conscience that informs you when you're about to do wrong or have done wrong. A good conscience is one that is active and sensitive enough (not numbed by repeat offenses and trained by knowing God's 'rules' - right from wrong). You may not always feel like you're a shiny, perfect person with a good conscience, but it's more likely to keep you out of trouble than a 'clean' conscience.