Wrong Question. A better Question is :
If the Government trusted the NSA with our every phone call and email, why should we trust the Government?
If the Government trusted the NSA with our every phone call and email, why should we trust the Government?
Imagine such a system in the hands of your least favorite politician and/or party. If you're OK with that, then by all means, carry on. Some of us aren't.
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.
However, you don't know and can't predict how the government will change in the future. Data collected today is data that can be abused tomorrow.
They don't want to be able to arrest everyone. They want to be able to arrest anyone. Data collection processes like Prism are an important tool.