What I am concerned about is the transparency of the arrangement overall. But if NSA said "Hey Guys, we're monitoring Facebook and G+, don't use those if you don't want us to be able to intercept with a warrant!" then that would defeat the purpose of the system entirely. So it's a difficult issue.

I will say that I would feel better if I knew what legal & policy systems they were using to ensure accountability. But honestly we know in general what needs to be done to keep dangerous systems like these used safely, I don't think that's actually the problem. We've kept nuclear weapons and bio-weapons safe, after all. But I would feel better if I knew that NSA had those kinds of onerous formal controls on when systems like PRISM were used.