Except you know, it doesn't prevent terrorist attacks. At all.
All it does is make the pile of hay with the needle in itthat much bigger. And a hell of a lot more expensive to the tax payer that is paying for the privilege of being spied on by their own government.
Mass surveillance is deeply contrarian to our core values as a democratic society. If it is to happen there needs to be a discussion and a public decision. That's exactly what is set into motion by the Snowden revelations.
The bulk approach leads to a saturation of data. That doesn't make things easier, it complicates them.
Terrorists are a few hundred, spread through the billions of people. Or, on the same kind of numbers, around 0.0000001% of the people the NSA spies on.
The usual justification for invading becomes ridiculous in that context: We need to restrict the people's freedom by spying on them, because we tried to bring freedom to another country.
"Big attacks" are vanishingly rare. But, just for the sake of argument, they haven't had an attack until they do.
The point of this is the US is actually harvesting way more data than the U.K., and we have so-called "lone wolf" attacks every couple of months.
Mass surveillance doesn't keep you safe.
Keep in mind that while we're trying to prevent terrorist attacks against us, we're actively and have actually used those same terrorists to further our goals in other countries.
I am not an American and I don't have a motivation to defend NSA or whoever, I just think that what Snowden did was partially wrong. Of course, caching the Internet like NSA and others are doing has human rights consequences, and those should be discussed publicly. But question the very existence of such practices is unreasonable in the situation the world is in nowadays. There are LOT of people in the world today who would want to wipe off the whole Western civilization, if they could... there must be a protection from them.