Ideally, you shouldn't be running around hitting anyone. Regardless of gender, y'know?
In other words, the average man is taller and has a higher percentage of muscle than the average woman (obviously there are going to be outliers on each side, but we're talking overall). So on average, a man hitting a woman has the capacity to do significantly more damage than a woman hitting a man.
Then you add in the cultural bit (which obviously has even more variety, but again, we're talking averages) where men are encouraged to be stronger and women are encouraged to be slimmer, and that exaggerates the basic biological difference, so instead of being just 15% larger and 40% more muscular, those guys are even larger and the women even tinier.
So I'd say it's a rule that works for the same reason that fighters fight in weight classes (and the reason there are sayings about not bringing a gun to a knife fight and the like) - it's rarely a fair fight. That it's sometimes a fair fight (and occasionally tipped in favour of the female) does not change the overall average of it.
I'd say that it's a rule based on average regarding sexual dimorphism in conjunction with socially-conditioned approved actives for different genders.. What I'm looking for, explicity might I add, is a reason not to do it. Those of you who deem it wrong please tell me why. I want to know the logic behind this train of thought. Don't simply tell me "Because." Don't tell me about how you personally don't do it. Or how it irks you the wrong way. I'm looking for a logical argument.
In other words, the average man is taller and has a higher percentage of muscle than the average woman (obviously there are going to be outliers on each side, but we're talking overall). So on average, a man hitting a woman has the capacity to do significantly more damage than a woman hitting a man.
Then you add in the cultural bit (which obviously has even more variety, but again, we're talking averages) where men are encouraged to be stronger and women are encouraged to be slimmer, and that exaggerates the basic biological difference, so instead of being just 15% larger and 40% more muscular, those guys are even larger and the women even tinier.
So I'd say it's a rule that works for the same reason that fighters fight in weight classes (and the reason there are sayings about not bringing a gun to a knife fight and the like) - it's rarely a fair fight. That it's sometimes a fair fight (and occasionally tipped in favour of the female) does not change the overall average of it.