Whenever you hear someone say something like, "I couldn't do that, my conscience would bother me too much," be suspicious. Generally, when someone advertises his conscience, it's a fairly sure sign that he doesn't have one.
For those of us who aren't sociopaths, we're not really aware of our consciences, certainly not as a separate entity. They're just part of us, built into our wiring, and we're no more conscious of them than we are of the way our nerve endings are connected within our brains.
In fact, the very idea of a "conscience" as a distinct, separate part of us is misleading. A conscience is simply the part of our personalities that makes us feel shame and embarrassment, and thus prevents us from acting on our every impulse. If we instinctively know that we would have those feelings after certain behaviors, it prevents us from engaging in them.
Sociopaths don't feel shame, and therefore don't have the same kinds of brakes on their personalities that most of us do. As a result, they often feel compelled to advertise their innate "goodness." They've heard of consciences, but don't really have any instinctive feel for how they work, and are thus more likely to refer to them as a distinct part of their personalities.
For example, when Casey Anthony's inevitable book comes out, expect her to say a lot of things like, "I was absolutely horrified when I first found out that people actually thought I might have killed Caylee. My conscience would never have allowed me to do that. I loved that girl with all my heart."
I got to know one sociopath on Wall Street very well. He was forever saying, "Hey, I'm the guy who's gotta get up and look at himself in the mirror every morning," as if doing something immoral would really have weighed heavily on him. This is essentially the same phenomenon at work: he had heard this expression, but since he never really felt guilt himself, he actually thought that it was the physical act of examining his own features that was supposed to bother him. So he used the expression. Over and over.
A normal person talking about a possible action that would bother him is more likely to just make a distasteful expression and say, "No thanks," or, "Yikes, that wouldn't feel right."