I tend to approach these questions with a bias towards a legal perspective. ;-) And for me, that means I approach it from a gender-neutral perspective for equal application of the law as much as possible.
I think that the idea that women should not be hit by men is intimately connected with ideas about gender roles that are, in my opinion, profoundly outdated. Equality means that women can be dicks as much as men can be, and should accept the consequences accordingly. The fact that men, generally, are stronger than women (an average that has limited applications) means only that in general, when you apply the rules above, it will be more often the case that it is not ok for a man to hit a woman than it will be for the contrary scenario. Just as opening the door for a woman, the man paying for a date, or requesting one, I feel like there’s a notion of “chivalry” the results in a general idea we should protect women.
Screw that…women can protect themselves (objectively).