We do have evidence that they conduct massive surveillance could be unconstitutional.
We do not have evidence that they are abusing this, and more importantly we don't know whether they have been able to save lives.
It could be that the people who work there know about positive life-saving results from the work they do and that's why they continue to do it.
(Edit: downvotes are fine, but it would be nice to also see a single link to evidence that the intelligence itself is being misused as opposed to protecting people)