Snowden is pointing out an issue. And he has done it with courage that I massively respect. You hardly see it these days. And that makes it anxiety and fear inducing, as the solutions are unknown.
But think of it this way - tomorrow someone might hand you a diagnosis of cancer. You can freak out about it or you can find a Cancer specialist to see what options are available. Asking the technician who gave you the report what the odds are, doesn't make any sense. He knows only how to create the report.
In this case just look to history, to understand how these things play out. History is the Oncologist.
Intelligence agencies have hard problems to deal with. On top of it, they are giant bureaucracies which means cockups, incompetence, turf wars, hiding issues are the norm. All that amplifies the problems, causes defensiveness, over-reactions and reactions to reactions.
If you read the history (and these days there are tons of resources) this sequence of events (of overreach) has unfolded a thousand times. There are a whole bunch programmes that have been shutdown because one group or the other got carried away or did damage. That history (in out current environment of over information/disinformation/misinformation) is what will always be a source of hope and faith.