The problem with that isn't that they are going to eavesdrop on the average joe - there's a lot you can do to take advantage from a surveillance system, politically, for example. Think Watergate... only it would have been as legal as Nixon needed it to be. Union leaders, businesspeople and small time politicians more or less unable to maintain their independence, you name it. Better not open that can of worms.
I believe we are talking about the FBI and the CIA running surveillance. These agencies aren't supposed to be involving themselves in politics and labor issues unless there is illegal activities suspected. The press would have a field day, just like with Watergate, if it came to that.
Not to mention the real charges in the Watergate case are the breaking and entering, and the subsequent attempt to cover that up. They weren't with the FBI or CIA, it was the FBI that pursued the case.
And really, today's politicians don't have privacy at all. They are under the public eye all the time.