Why do women find dangerous men exciting and sexy e.g. guy with a motor bike?

Actually, it does make sense from an evolutionary point of view. Back in the days when we were all living in caves, resources were scarce and individuals had to fight hard to get what they needed. In such an environment, men who were rough, brutal and aggressive had an advantage. Society has changed a lot since then, but biologically we are still the same men and women that we were back then. So, when a woman sees a man who is bad, aggressive and dangerous, her subconscious primitive instincts say "strong male, good mating material" even if she knows better from a rational point of view.