Striking back does not necessarily mean physically, nor does it mean it has to happen immediately. An indiscretion that goes unpunished will encourage the attacking party to continue doing it. Especially in a work environment.
Being unwilling to treat others like they treat you could be seen as a sign of weakness. However, of course, one must be able to see the masochists for who they are, and avoid accordingly.
Interacting with people is a most complicated dance of wit, intellect and emotion, that can easily drive all but the most skilled to the point of insanity.