I don't like the idea of police using entrapment for victimless crimes, but in cases of conspiracy to commit violent crimes, I think it's in everybody's best interest to lead those dipshits to their just deserts. Granted, there's always the chance that a disturbed person, who would normally not consider violence to be an option, might be "influenced" by the cops to change his attitudes regarding that option, and in those cases we have to hope that the cops are playing by socially acceptable rules.
As they're so well known for doing? It's become socially acceptable through arbitrary dictum, just like corporate personhood. If there's always the chance that a disturbed person..... then there's reasonable doubt that the police weren't the "but for," that they weren't entrapped. It's easy to find a group of religious people and motivate them to violence. The FBI is a bit like Hamas or Hezbollah, radicalizing people, offering support and encouragement to terrorism, but worse because presumably those organizations are sincere and don't go "lol, jk. You shouldn't have taken the bait. Now you're fcked, friend"
Like I said, since they're apparently always limited to buying the items necessary to commit these crimes, ie the bombs, from the actual law enforcement doing the "investigating," that suggests they're only possible because of law enforcement involvement. Maybe they should target people who have the means and pre-existing intention of commiting terrorism and not merely those easily manipulated. They befriend these guys and earn their trust, and they have careers to advance, and the type of person who would take these kinds of assignments tend to be of questionable character.