Nothing to hide is an incomplete sentence. Nothing to hide from who? Surly 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 some 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.