Just want to point out the key problem with this type of justice: sometimes the accused is actually innocent. I have no idea what the rate of false accusations in molestation cases are, but you'd feel pretty bad if you "offed" someone only to find out that (i) your kid just made the accusation to get attention, (ii) the detectives were a little too aggressive in interpreting your kid's description of what happened, or (iii) it was a case of mistaken identity. All of those things have been known to happen.
I'm certainly not saying I think that's what happened in this case. (In fact, IIRC it was pretty open and shut case, so I don't shed any tears for that guy.) However, the reason we generally don't like people taking the law into their own hands in our society is that sometimes the vigilante turns out to be wrong. When that happens, a single tragedy can turn into two tragedies.
Having said all of that, I've got no problem with putting child molesters in prison or mental institutions for life once convicted. The residivism rate is large, and the crimes generally get worse -- especially since they don't want to get caught again, and there's usually only one witness...