I had this discussion with someone tonight. I don't think Michael Schiavo HAS a conscience.
There are people out there who really pretty much don't have a conscience. Externally, at casual glance, it can certainly look like they do, but it's only because they've learned that's how they're supposed to behave. They're actors. Their apologies, if any, are theatre and their tears are crocodile tears.
Once you've dealt with a couple of these people at close range and had your life ripped to shreds by them, you start learning some of the subtle signs by which you can recognize them.