Death penalty

It would depend on lots of other factors but in theory if you killed a bunch of murderers and compared that to getting them wander randomly you would save lives - if you chopped their legs off instead (or gave excessive electro-shock therapy or whatever) you would achieve the same aim and save one extra life.

So I argue that making the criminal unable to commit the crime is in a sense fundimentally superior to the death penalty. Better yet they serve as a walking billboard for why not to commit the crime.