Nothing to hide is an incomplete sentence. Nothing to hide from who? Surely you want to hide your children from abusers and predators? Don't you want to hide your banking details from con artists and fraudsters? Your identity from identity thieves.. Your location from burglars, your car keys from car thieves or your blood type from rich mobsters with kidney problems..
we don't know who are any of these things. So we should protect ourselves from all of them, in effect we have everything to hide from someone, and no idea who someone is.
edit; let me just add the obvious, that the government and police, Google and Facebook, are made up of many someones.
Its often that we see something thats wrong, but we struggle to express why. This does.