I don't really want to get into it that much either, but I will say if they aren't dealing drugs, then no one should get arrested.
It's about intent. If someone goes up to a cop and
intends to purchase illicit drugs, that's criminal behavior and I don't see any problem with arresting someone for it.
I still don't really agree. You are still somewhat encouraging them to commit the crime, even if they were willing to do it.
They're on public chat rooms having extremely lewd, sexual conversations with minors knowing that they're underaged.
Even if the minor begin the discussion, any sensible person would ignore them once it becomes sexual. Someone who's a little disturbed might cyber, and then end it there.
But these people? They make arrangements to meet an underaged girl at her home, alone, and then go through with it. This isn't an immediate decision they're pressured into. If at any point they were willing to reconsider their actions, they had all the time in the world to change their mind on the drive other there.