Why do we think it's okay to completely stigmatize certain groups?

Certain groups like pedophiles, offenders, etc. are so stigmatized right now that people are constantly saying things like they want to kill/beat/basically lynch these people. Why don't we put more effort into getting these people psychotherapy than making them into social outcasts and forcing them into hiding. I mean, I see the anger that arises from molesting kids, , etc. as those are very harmful things, but I think the more we stigmatize it, the more afraid people are to seek help for these things or admit to them, and the more they still do it but do it undercover, and seek support networks to counteract all the negative stigma, instead of seeing it as a problem that they can be helped/cured.