Scroll down to Feb 20 and look at the rape rate graph. Note the sharp drop when CCW was permitted on college campuses.
Now look at this:
Well, why not?
Update: The drop is unexplained, but the graph above suggests that humans will kill a certain percentage of their fellows at a rate that doesn't get below a certain level.If guns are not available, other means will be found. We are clever monkeys. Go here for a more complete report.