I've seen a one guy sucker punch another over a woman, dropped him straight to the floor. All three were total strangers to each other, also everyone was probably drunk though. I agree that it is unlikely, but it isn't beyond the realm of possibility... also to assess the violence situation you have to factor in the crowd. If you're going to potentially start shit it matters if you happen to be surrounded by his friends.

Anyway, although I agree with treating unwanted advances with reciprocal escalating naked hostility, the meetup organizer is really the only one with the power/knowledge to enforce standards of behaviour.