Cruel and unusual punishment is a basic violation of human rights that the eighth amendment prohibits. Do you really want our society to encourage barbaric behavior?
Towards slavers and child molesters? Yes.
Other than satisfying your revenge fantasies, what does that accomplish?
Incidentally: Child molesters are possibly the most convenient bogeyman, after terrorists. Anyone criticising your latest internet censorship bill? Just frame it in terms of stopping child pornography! Now everyone who disagrees with you is siding with the paedophiles, and is probably a paedophile themselves.
Declaring one particular segment of society as Designated Pure Evil, even one as obviously evil as child molesters, creates a powerful mind-killer. I.e. a topic where any related discussion is that much harder to be approached rationally, because the powerful emotional associations dominate every other aspect of the conversation. Godwin's law is the obvious example: the Nazis are the go-to Clearly Evil group, so anything that can be remotely compared to Nazis, no matter how irrelevant the comparison, is automatically evil.
Passably rational discussions are rare enough as it is, no need to give people any further excuses to immediately shut-down their brain when encountering subject X. And that is exactly what you contribute to when you argue, seriously, that child molesters should be tortured. It's not a useful deterrent, it doesn't undo any of their actions, it doesn't stop them any better than prison does, all it does is give a short-term sense of satisfaction, create pain, and encourage simplistic thinking.
Hell, let's be generous and assume that pain suffered by evil people is irrelevant, or even a positive by itself (I disagree, but I can understand the impulse). What happens when, inevitably, someone is wrongly accused of being a child molester? It's a difficult accusation to defend yourself from, because of all its mind-killing aspects, and eventually an innocent will end up tortured. What is the guilty-vs-innocent ratio you're willing to tolerate, here? How many guilty child molesters should be tortured, to offset the negative of one innocent person being tortured alongside them?
And, yes, the question is rhetorical. I don't expect an actual number. I'm just trying to get across why it's a bad idea for a civilized society to encourage barbarism, even against the obviously evil.