Women love it because it turns them on. Simple as that. They get off on being overwhelmed, used and abused, taken, made to feel small, and all that. That's just part of being female, loving the power imbalance, the contrast between masculine and feminine. I don't think many really think about being protected from intruders when they get wet at their dude smacking a bitch. You can tell her to shut the fuck up, and that feeling of humiliation might be accompanied by arousal. Actually, I'd even go so far to say that the guys they feel the safest with are those they are the least attracted to, not the other way around.