Um, I'm going by the scientific route as we do seem to know why a person, not even a man, rapes. The chemicals in the brain are already messed up in how they think and consider others lives and how they affect them. So rape, for them, mentally from birth, isn't a "bad" thing in the way the rest of us see it.

There is some debate on the nurture aspect. Again, this is from the angle of all genders. Cause females do rape as well. They were abused at some point in their life, usually sexually, and perpetuate that violence because the brain was damaged in the process of the act.