So, to summarize:
1) Many people are violent and it's not a single gender issue at all, an average man is only slightly more aggressive than an average woman..
2) Most domestic violence is reciprocal (measurably). Yet
even people with amazing track record on fighting against domestic violence run into insane trouble for stating that.
3) Men are indeed stronger than women and, on top of it less susceptible to physical damage, i.e. even stronger women would get bruises easier than weaker man.
4) There is
no equality in the way we
reproduce, without exaggeration
women are 100 times more valuable than men. Perhaps that is the reason why even when aspect #3 is taken into account, humans (both men and women, although women more) care much more about women,
measurably. (and, don't get me wrong, I do think that it does make sense)
5) On top of it, it's not simply a woman, but a pregnant woman. On the "who do we, as a species, care about" scale, basically unbeatable.
Our opinions are perfectly cemented in laws. In the same situation reversing gender can get you from guaranteed jail time to slap on a wrist (e.g. shoving a broken bottle into guard's face). Is that "equal"? Nope. Now check #4 again.
So, obviously, In scenario when a dude quietly sitting there touching nobody gets attacked by a pregnant woman,
he has no real option, but to give in.
I can understand people getting very upset about attacking pregnant woman in front of the kids as well as people thinking "hey, way a second, how is that fair, it was she who started it!!?".