I've always been raised to believe hitting women is fundamentally wrong. The only time that view doesn't hold is when a woman is acting in a violent manner first, in which case the rules go out the window.
However, I do think as Nerdygirl says, there is a difference between abuse and violence. Emotional state at the time also plays a part.
Say my girlfriend is at my house, I've just been diagnosed with a serious illness and I'm about to tell her. Then she tells me, before I can, that she's been having an affair for a year.
Now, if I were to snap and hit her at that very moment, would it be domestic violence? Yes, and it would be unacceptable. However, people often do things that they would never otherwise do if they were thinking straight when they are emotionally worked up.
I personally think 99% of cases of domestic violence are completely intolerable and are generally down to a man or woman's emotional or moral weakness. I'd hope that even if I was really heartbroken or enraged, I'd never stoop to the level of hitting a woman.
However, every now and then there is rarely a kind of emotional impulse that overrides reason. Kind of like those temporary insanity pleas you often hear in court cases.
It's never right, and I think most scenarios are downright disgusting, but I think it's not possible to just say "Yeah, X is always wrong no matter what the circumstances."
