I spent 33 years with the Agency, almost all of it on the tip of the spear, 22 years overseas. In my job I would’ve seen intercepts between US persons. I never saw ONE. We were continually reminded of our responsibilities under the 4th Amendment; a violation could result in dismissal or prosecution. If it went on, it was pretty well hidden.
Unfortunately, between Snowden's revelations, and with the decay of the Zeitgeist into what I call "the Era of Bad Stewards", I'm not so confident that all those now in the NSA are serving as honorably as you did in your 33 years.