Generally, you're not suppose to hit anybody. The exception is self defense, where you can hit somebody to the degree necessary to stop the attack or get away.
That being said, boys and men have been taught over the centuries that women are incapable of defending themselves and precious and it is the height of cowardice to hit a girl. That didn't come from feminists, that's been true for centuries. It is an outgrowth of "wombs are precious".
The problem, of course, is that you don't think when you respond to an attack. Many people will respond to a physical attack with as much force as they can muster, which in the case of most men against most women is overwhelming.
That is, women are more likely to get hurt worse if they incite the domestic violence than if the guy does.
The point is, yes, there have been a few (very stupid) feminists who have attempted to incite riot with the cop-out of "you can't hit me, I'm a girl" and, in doing so, totally lost their credibility. It is a stupid thing to say if you actually want to promote the cause of feminism.