But as you mention, that monopoly on force is tied to the will of the people.
If the government were to use force in a way other than approved by the laws setup by the peoples' representatives then you're already talking about something much worse on the totalitarian continuum than phone metadata.
And at that point, once the law has no limiting effect on the government anyways they could setup things hundreds of times worse. But they would hardly need to, as they could manufacture evidence of supposed "crimes" if need be and carry out sentences of their choosing for any reason at all.
They would only need things like Prism for dissidents, and dissidents would already assume that things hundreds of times worse were in place and take defensive measures accordingly.
So you're right that the monopoly on force is dangerous, but it has always been so. That's why it requires that tremendous system of transparency, accountability and oversight that you mention.
But given that we're able to provide those controls in the first place (controls which we cannot enforce on private companies, btw!) it makes sense again to ask the question of whether programs like these are both reasonable and effective, whether they can be properly supervised, and if so whether current systems are "proper supervision".
"Monopoly on force" is a warning about government, not the NSA. And especially not in the context of knowledge, where the government is mostly far out of its league compared with the private sector, and it's only getting worse.
