You so sure about that? Last I checked, congress was more or less in the dark when it came to a lot of the aspects revealed by the Snowden leaks. Furthermore, what's to say they can't simply misreport what's actually going on? They only give information on a voluntary basis, and being in "contempt of congress" is simply verbiage. The FISA court rubber-stamped them to collect almost any data, even of US citizens, in "good faith." What's to say that data doesn't contain details of those in congress -- incidents that would threaten their reelection? It creates a very vulnerable relationship where the NSA could more or less do as they please.
Again, these aren't per se accusations of current behavior, since we really have no idea, but they're suggestive of future misuses that are bound to happen in time.
The only one who actually knows what the NSA is up to is themselves.
those committees authorize the NSA budget and congress people have always hung the workers out to dry with full knowledge of what they had done if the press is against them at the moment
if the head of the NSA is trying to blackmail you on knowledge you only gave to a very few trusted people, what does that tell you? what is going to happen next time the next head of the NSA has to be approved by the senate?
the government used to do a lot worse in the 70s to people they didn't like