Mariano,You believe that you have found the silver bullet--the argument that allows you to plug your ears and go "la la la la la" to whatever any atheist has to say about morality. Well, you haven't.You presuppose moral realism and then reject alternative interpretations of moral statements without consideration, simply because you cannot comprehend a reality without objective morality. Morality can't be subjective because then it would be subjective--you're content to leave it at that. Please consider the possibility that you might need to put a little more thought into the matter.In your last paragraph, you basically say "I don't have to listen to you because I can pretend to be a psychopath that doesn't agree with you that mass murder is actrocious." My response is: so what? Why should my inability to convince a psychopath worry me at all? You seem so concerned that we won't be able to figure out who is correct, me or the psychopath. But unless we presuppose moral realism, the question of "who is correct?" doesn't even make sense. You might as well ask, "Which is heavier, green or blue?".You see this as a problem. Please explain what the problem is. If you think it's too obvious to even mention, please mention it anyway. Pretend I'm seven years-old. What is the actual, practical problem with a reality in which morality is subjective?
Mariano's objection to subjective morality is roughly analogus to saying that if our sense of how much light is subjective then whether it is day or night is just a matter of opinion. Yes, a crazy person can state that midnight is brighter than noon but it would be silly to actually argue with that person. On the other hand, reasonable people can have a different evaluation of when twilight should be call night.
Oops. (I seem to be having trouble proof reading my posts before hitting the 'Post Comment' button.) In the first sentence it should read: "...our sense of how much light there is, is subjective..."