There's no need to qualify that with "many authoritarian or the like use". There's no way to know whether or not PRISM has had any impact. Even if the program were to stop today, if everything remained the same, you could still argue that the effects of the program were so great that they've essentially collapsed the US-targeted terrorist attack industry, possibly forever.
The only real discussion that can take place is whether or not the potential safety afforded by the surveillance is worth the real erosion of freedoms. Those in favor of the surveillance are winning that discussion where it matters, whether its through emotional appeal, fearmongering, corruption or whatever. Its a totally opinionated case at this point, which even the ballot box wouldn't help as you'd just be shifting the onus of persuasion from the military leaders to the American people, who definitely don't know enough of what's happening overseas to make a reasonably informed decision.
Its the most complex issue voters would be straddled with, everything pales in comparison.