The decision to kill would an act of defense. Organized sex trafficking preys on members of a community. If you see it happen, stop it. If that means killing the perpetrator, you’d need to justify it to your community, but you don’t have to kill them to stop it.

The argument you use there is the same argument used for genocide "We had to defend ourselves from X who are corrupting our society and way of life!". The appeal to community only works if the community doesn't hold prejudices against others.

But further, not how sex trafficking/child porn works. It's not this secret cabal of kidnappers stealing babies in the night. Sex trafficking is almost always perpetrated by a trusted individual. Where this gets real bad is cults like the Oneida cult which pushed for free love of children. And this gets back to my original point, how does the community address a problem when the community IS the problem?

Both of those systems would thrive in a libertarian model and they would have a lot less red tape to contend with in order to liberate the cult members.

Red tape is not what stops people from addressing cults. It's actually funny you mention Jonestown and mormons because both movements famously relocated their members to escape government control and interference. So you are saying that a libertarian model with even less government control would somehow end cults faster? I really suggest you read up on how cults function and move because quiet literally they are hoping and looking for libertarian areas to setup shop. Cults LOVE to pick and take over small remote locations precisely to escape the pesky government red tape and oversight. (see: Rajneeshpuram as an example).

What checks to cults do we currently have?

Not enough, but more than you'd expect. You can leave a cult, sue it if they start tracking you. Cults that abuse children (such as the FLDS) can be dismantled and their leaders arrested. Cults that physically harm or imprison their members can be subjected to legal actions (which is why scientologists put their member prison in international waters). Certainly the current system isn't perfect, slow evolution is the nature of centralized governments. However, that slow evolution also (usually) prevents overreaction.

Why hasn’t the state eliminated cults if they’re so capable?

It's not a question of elimination. You can't eliminate cults anymore than you could eliminate religion itself. (and, in fact, it's likely easier to eliminate religion as there are non-religious cults). The question is one of harm reduction to citizens. One of checks and balances to make sure the state isn't overreaching while simultaneously penalizing organizations that do. It's a game of cat and mouse, ultimately. The issue is these are things only fixed by regulation. Take away all the regulation and you are basically just saying "Well, hopefully that cult will sort itself out".

Jonestown is a really good example of why just leaving them alone is a bad idea. Jonestown happened because the leader of that movement became so paranoid that when a senator visited the community, that was enough to have him push for mass suicide.

Just for your future arguments, ruby ridge is a much better example of centralized government absolutely doing the wrong thing.