Well it couldn't hurt as the overall population of child molesters would significantly drop.
I don't think anyone here is against child molesters dying, it's just a really dangerous thing to allow vigilante justice. If you allow one person to get away with it, someone might kill someone for something else they see justified, then you have a whole bunch of people taking the law into their own hands.
Look at Sandusky.... how many decades was this guy getting away with child molestation? Something is really messed up that these cases happen. I'm not sure exactly what the solution is, but it is clear that there is room for improvement, and a need for proactive measures that go beyond our society's traditional measures. It does not appear that the threat of punishment in itself is sufficient to prevent bad actions.