I think the answer to that is long and complicated. But a couple of things readily come to mind: First, since sex is inherently dangerous for a long list of re

I think the answer to that is long and complicated. But a couple of things readily come to mind: First, since sex is inherently dangerous for a long list of reasons, I suspect humans will never entirely escape an association between danger and attraction/sexiness. Second, bad boys aren't necessarily a threat to her. Instead, they can very well be a threat to the control other people wish to exercise over her. If "good girls don't," then a "bad boy" can be the solution. In some sense, he takes the blame for her "bad behavior" of getting her sexual needs met. Bad boys are often men who do not respect the social norm that if a woman is in a relationship, she is off limits, not out of respect for her, but out of respect for her man's property rights. A bad boy who treats a woman like an actual human being in her own right, and social norms be damned, can be not only a good partner, but the best antidote to some really toxic social norms. The assumption that societally labeled "bad boys" are really bad people is a pretty one dimensional view of a very complicated thing.