If the spy methods are not actually reliable, they should not be used, goes without saying.
But like with terrorism, we don’t have to inform the rest of the terrorists what we are privy to.
I believe the kicker here is that the reason the feds are able to ID these people is because the feds are running most of the CP sites to begin with, and are promoting these sites as entrapment schemes. As effective as this might be it’s totally illegal, because of course the fact that it requires promoting and distributing said content.
After what we have seen these agencies do, there’s no reason to believe anything they assert is on the up-and-up without seeing the whole of the facts.