A little research on the web suggests why illegal immigrants from Mexico (and perhaps other countries south of the border) seem to have such a high rate of these types of crimes. The machismo culture that sees women are less than men, an age of consent of 12 in many (and no more than 14 in any!) Mexican states, and an attitude by the legal system that rape is just not that big a deal.
People bring their culture with them. This is a part of the culture most of us would not celebrate.