To give a more extended opinion on this subject, I would say sexual abusers are complex individuals. They are not what you would call legally insane (they do not suffer from psychosis), but from that to say that they are sane, I really think I would disagree. As a psychology student and a human being I consider therapy and treatment the only possible way to bring back to society any type of agressor as long as it is possible. And that's what I think prisons are for, to rehabilitate people. That said, if it's not possible, I think those people should never be let out, until the day they really are rehabilitated. If someone is rehabilitated there's no real reason for them to be in prison (I'm talking about severe crimes here).
And just in general, revenge is not justified under any means when you want to look at yourself in the mirror and think you are better than a rapist or a killer. I know people are in different stages of developement but I will never understand how a good human being enjoys thinking about revenge of any kind.