Often the events that create a hardened criminal are ones you cannot hope to fix, or in many cases even detect. There are warning signs for, say, serial killers (an example I know a bit about) but they're hardly gospel pieces of evidence, and certainly wouldn't stand up to close scrutiny if they alone were the basis of a charge. And I have issues with the state having the power to legally execute people anyway, so in such a case, prison really does seem like the best solution.
That said, I think the majority of white collar and victimless crimes do result in pointless jail terms because of a lack of imagination or out of a desire to be seen as "tough" on crime.