I have a similar feeling regarding PvP games. Not so much for any simulated violence, but rather for reinforcing the zero-sum philosophy of, "For me to win, another human being has to lose." However, I don't feel the same about many non-RPG, zero-sum games, like chess or poker.

Maybe because it's easier to be detached from cards and plastic pieces, than from a character in an RPG - who has a name, 'friends', a pet, a history of achievements, etc.

You can call me a "care bear", but I personally don't feel that reinforcing such a limited world-view is how I want to use my time and energy. And it's not something I describe as fun.