There is some ineffable something in those who are distinctly uncooperative with requests to define morality or otherwise have a rational discussion on the matter, both here and on all forums where I've discussed morality, and I think you've hit on what that something is. It is the fear of nihilism, the fear that without their moral compass they might suddenly want to do evil, deplorable things because they'd be A-okay.

What they don't see, in my opinion, is that it is their very dread at such a possibility that is really what is keeping them from doing those things. "Morality" provides no additional protection; it merely serves as after-the-fact justification of the sentiments that were already there.

We don't cringe at the thought of stealing from old ladies because it's wrong, but rather we call it wrong to steal from old ladies because we cringe at the thought.