"As a way to ensnare users, the FBI even took control of Playpen and ran it for 13 days before shutting it down." Shouldn't the agents running this site be charged with child pornography distribution? Or are they above the law? This would be a full blown investigation against the police in this country (Norway), but here entrapment is illegal too.
Unfortunately we've seen that law enforcement in the US is able to get away with doing some rather despicable things in the name of fighting crime. Personally, I don't believe it's moral or ethical for law enforcement to commit crimes in order to catch criminals. After all, how can we defend our own morals and ethics if we're willing to ignore them for "reasons"?
I think you want to look at systemic effects and the potential for bulger-style corruption. Distribution of child porn does not do direct harm. It does harm by being a system that supports child abuse and we have collectively decided that child abuse is harmful enough to the fabric of our society that it is worth dismantling the systems that support it.
So here, the ends justify a certain scoped set of means, but also impose a duty of competence in deploying those means and a duty to stay within their scope.
Note that We don't currently have any penalties for crossing the bounds of that scope.