The whole "secret court" thing is FUD. The FISA "secret court" was created by law to insert itself into a process that didn't require a court proceeding in the first place. It's not empowered to adjudicate peoples' rights and obligations.
As for "secret court" that you put in "scary" quotes. Just to be sure, no one says secret as in no one knows it exists, but that the public is not allowed to know what it does. Which is not FUD, some of us see that as a clear problem.
And we know what the FISA court does--it reviews requests by intelligence agencies to engage in foreign surveillance, as provided for by the FISA Amendments Act. It does not put people in jail. The biggest misunderstanding about the FISA court, a misunderstanding rooted in FUD, is that it has the powers of an ordinary court and uses them in secret. But unlike a regular federal court, a FISA court cannot adjudicate your rights and obligations.
What Congress did by creating the FISA court was to insert the judicial branch into a process, foreign surveillance, that, Constitutionally, does not require judicial branch involvement. Its proceedings can be secret only because it does not exercise the normal power of the judicial branch to determine peoples' legal rights.
The problem, as I see it, is the secret of exactly what they are doing in terms of American people and/or businesses that require they place gag orders on nearly everything they do.
I wouldn't say that they "sentence" people as in a normal court of law, but what happens if you defy one of their orders? If I were to ignore their gag orders then they'll just say "oh well, too bad for us"? The reason we don't know what happens in that case is because, as far as I know, no one has openly defied the orders.
Notice I said the Justice Department, not FISA, knocks on your door.
Saying this court throws people into secret prisons via secret orders enabled by secret laws is, of course, FUD. But then, I'm not saying any of that at all.
/snark