I was going over the Sequences on metaethics, and it was leaving a bad taste in my mouth. The examples are all about killing or saving children (both of which are far outside my personal experience). The assumption is that the participants in a discussion about metaethics are, in fact, moral in the normal sense of the word. That they're talking about justifications behind beliefs they actually act on, like not killing babies. That, when the philosophical discussion is over, they will go back to being basically good people, and so part of the purpose of the philosophical discussion is to explain to them why they shouldn't stress out too much. If there were no "morality," you still wouldn't kill babies, Eliezer presumes. Philosophy is just so much verbal dressing on something basically secure.
But my situation is a little different. From time to time, like Pierre, I don't care. I get emotionally nihilistic. I find myself doing things that are morally awful in the conventional meaning of the word: procrastinating, sneaking other people's food out of the communal fridge, being casually unkind and unhelpful, breaking promises. I don't doubt that these are awful things to do. I figure any moral theory worth its salt will condemn them -- except the moral theory "I don't care," which sometimes seems strangely compelling. In an "I don't care" mood, I generally don't care about the truth or falsehood of factual claims either. What does it matter? Penguins are green and they are a deadly menace to human society.
What I want to know is: what goes through people's heads when they're motivated not to be awful? What could you tell someone as a reason not to be awful? If you are, in fact, not awful, why aren't you awful?
Edit: the kind of why I mean is not a justification (Humans have natural rights to life, liberty, and the pursuit of happiness) or an explanation (Humans care about the things evolution leads them to care about.) I'm talking about an internal heuristic or a gesture at an intuition. What do you think, or feel, when you care about things? What would you tell someone who claims "I just don't care" if you wanted to get her to care? What would you tell yourself, in your nihilistic moments?
Feeling like you're a good person, or at least like you can make a credible case for being one, is an essential reward for most people. I don't see it as either psychopath vs. normal; on a continuum, some normal people are more willing to sacrifice this reward than others.
It's also easy to imagine being comfortable with acts of great malice or selfishness from a safe distance (e.g. hypothetical scenarios where there's no possible downside for you personally except the memory of having done evil); when actually in position to pull the trigger, empathy or caution will become more telling. I wouldn't become overly concerned with this sort of moral abstraction.
To imagine being content to do great harm to others, you have to imagine being extremely compartmentalized and delusional (in order to maintain the satisfaction of feeling like a good person), or else extremely unhappy. This is unattractive, and I can't imagine anyone choosing it who values clear and honest thinking about their own nature, unless their situation is desperate.
People who actually don't feel bad when they harm others are ultimately going to be extremely cautious to disguise this if they're intelligent, but wherever they're sure of some great benefit and can act with impunity, will likely do so. I don't rule out such people choosing to live by some strict set of ethics, but generally they're better off only pretending to do so unless they find deception especially taxing.