I mean, we have no idea what intelligence agencies "generally" do. What we do know is that the few things that have come out about their actions have been full of illegal things. So saying they generally don't do that isn't worth very much
We do have an idea of what intelligence agencies do. They collect intelligence. The FBI investigates domestic federal crimes, mostly child porn, domestic terrorism, and white collar crimes, among a lot of other things. The NSA has a more foreign directive and focuses on national security. The DEA focuses on the war on drugs.
A big problem I'm noticing everywhere is that, while we have access to all of this information on how the government works, no one exercises their access to that information before commenting on internet forums and spreading misinformation and doubt about our DEMOCRATIC institutions. Even if you don't elect the person who heads these agencies, you do elect the person who appoints those heads.
https://apnews.com/article/33a88feb083ea35515de3c73e3d854ad congress isn't sure what the nsa is doing, you will have a very hard time convincing me that the average American can know. We have broad overviews of their job directive, yes. And is this democratic to you, when they lie to congress? I don't believe it's very democratic anyway considering our first past the post system mandates only two political parties, and neither party has any interest in curbing the surveillance state.
If that's the evidence we have, that's the conviction they receive. It's pretty damning evidence. If an agency is willing to go that far, why give them the benefit of the doubt that was only thing that "got away from them"? Something like that only comes along when a systemic level of rules flaunting is prevalent.