So very worth a read (go read the whole thing):
Some years ago one could have argued that there would be restraint in the use of such powers. But no one can seriously make that case anymore. We all know they would do that sort of thing if they could, because we’ve all read of too many cases where they have.
Once the tool exists, it will be abused. I really wish I could say otherwise. I wish I lived in a country where law enforcement acted with the square-jawed nobility of a comic book FBI agent. I used to think I did live in such a country, but in recent years I have been forced to realize that I don’t. I think that, in your heart, you know it too.