In a broad sense, it's very hard to argue that selfish genes don't explain most human behavior. Certainly, I would spend my time differently if I weren't the result of a couple billion years of brutal gene-versus-gene competition.
Furthermore, humans have language, and can even ask themselves questions like "what would so-and-so do?" Our minds are filled up, it seems to me, mostly with the thoughts and data supplied by others. So I wonder if it makes sense to say that we are all individual minds.
Certainly a complete sociopath will still have non-selfish internal organs. But it's highly reductionist to claim that a sociopath is not sociopathic because his heart generously pumps blood to his other organs.
What looks like generosity generally falls into a few categories of gene-level selfishness, e.g. kin altruism, in-group altruism, reciprocal gifts, etc. Our evolutionary inheritance doesn't allow for pure altruism; that's a bug that gets fixed by selfish groups out-reproducing.
I'm also making a more subtle point about the difficulty of delineating where a person ends and society begins. This is a much fuzzier concept for me, but I have a hunch that it doesn't make sense to say that a human personality is entirely contained in the body that we normally associate it with, any more than crashing waves are contained within a rocky shore. The body gives rise to this funny thing called a mind, and yet minds don't seem to be stored just in one brain.
I did not understand your point about the sociopath; it seems to be making my argument for me, that the driving forces at one level of organization tell you little about the next level up.