I've written about this previously on LessWrong:

He isn't me. He is a separate person that just happens to share all of the same memories and motivations that I have. I want to say that I wouldn't even give this copy of me the time of day, but that would be rhetorical. In some ventures he would be my greatest friend, in others my worst enemy. (Interestingly I could accuratly tell which right now by application of decision theory to the variants of the prisoner's delima.) But even when I choose to interfere in his affairs, it is not for directly self-serving reasons - I help him for the same reason I'd help a really close friend, I hurt him for the same reason I'd hinder a competitor.