I think the persistent issue is the identifying US/non-US partipants and the co-mingling of US/non-US participants within exchanges, and the need to understand context to make sense of it. This seems inescapably fraught. And further complicated by their desire to still pursue Americans for inadvertently discovered crimes, resorting to parallel construction to avoid revealing questionably obtained evidence.

Parallel construction is a great euphemism for "knowingly and willingly breaking the law, then deliberately lying about it".

They're literally professional criminals.

You'd think.

I honestly don't get spying/law enforcement's desire to do unconstitutional things. Most of them take oaths to uphold the constitution, and there's apparently a lot of training about it. So why do such strong guardrails have to be put in place? I would assume that NSA/CIA/FBI would recoil in horror from violating constitutional norms, but it seems just the opposite - they're itching to just mine the data and put people away.

Everybody's the hero in their own story, and heroes don't need guardrails because they would never do anything unjust, at least not without a really good reason.

Yep. And in their minds the person is guilty (and sometimes really is) and the Constitution is preventing them from a conviction. It makes intuitive sense because the system was built on Blackstone's Ratio, so it's designed to let guilty people go free sometimes to avoid convicting an innocent. To law enforcement people, this would be massively annoying.

Even when they genuinely have the best of intentions. I'm not sure who causes more harm, those bent on destruction or those stridently doing "good." They cause similar horrors. It's a wonder humanity persists.