Firstly, yes, cut their goolies off.
Secondly, I have (as I've admitted before) a strong hobby interest in martial arts - specifically I teach and practice a form of Jiu Jitsu.
A friend of mine runs a big Jiu Jitsu centre in Bedford - quite a severe and dangerous form of the art. Yet, the local social services refer problem kids to him, they've shown that what he teaches them is exactly what they need to calm them down, make them more sensible, and stop them being violent outside his training hall. Counter-intuitive, but damnit it works!
So, more than likely some variation on national service might work. Failing that, a few hours locked in a room with a martial arts instructor seems to do the job quite well! Possibly it's a rapid creation of the rules-framework that was being talked about earlier, together with a "better" appreciation of what violence and helplessness feel like the other way around, albeit delivered in a controlled manner!
G