They could be invasive, by monitoring even when there's nothing going on, but there are well-defined rules and strict protocols in place, and I have never heard any cases where they have used the data to attack anyone personally or are there?
[0] - https://www.reuters.com/article/us-usa-surveillance-watchdog...
That's just the stuff we actually heard about.
NSA finds something out illegally, unethically, they pass it to another agency so proceeds to figure out a way to "discover" what the NSA did in a way that is legal, or at least plausible to the courts, thus never having to admit the investigation started with the NSA