The single biggest problem with “Why are you worried about the authorities monitoring you if you’ve got nothing to hide?” is the built-in assumption that the monitoring authority is doing its job without corruption, malfeasance, or other malevolent intent. There’s a reason they put the Fourth Amendment in the Bill of Rights, and it’s why people make a big deal about “probable cause,” warrants, and the like. It is as much a firewall against tyranny as the rest of the Amendments.

Given that there has never in the history of the world been an authority not tainted by the evil side of human nature, we cannot trust any authority with that much power. The Founders knew.