I don't buy that for a second. Having firsthand knowledge of how terrible our border security is, how much theater goes into our domestic security, and how half-assed all these show layers are, there's only one reasonable conclusion:

The number of humans on Earth that want to kill large numbers of other humans is exceedingly, vanishingly small.

Most people just don't want to blow people up, no matter how angry they are.

If this were false, we'd see bombings, shootings, and poisonings constantly all over the country. We don't.

I grew up in Detroit. Trust me when I say that this country has no shortage of machine guns.

If these sorts of things were being stopped by the NSA's dragnet, they wouldn't have claimed to have stopped "dozens" of attacks with their surveillance. They'd have claimed "hundreds" or "thousands". They didn't.

There just aren't that many people who wish civillian populations harm, even if their government did blow up their loved ones.