Another is also probably the argument of "nothing to hide, nothing to fear".
People always forget that you have nothing to hide if you know what they're looking for. The problem is you don't know what they're looking for. And the thing they're looking for can change over time. And once you've given it you can't take it back.
Not to mention that while you share it with one party, they'll sell you off.
People always assume nothing to hide means not doing anything illegal that'll make you end up in jail.
They think there's somebody going through all the data and that this would be too much work. They really don't/won't understand that computers have been able to do this at scale for years.
If any bigtech company does it it's fine. But if I ask them for their unlocked phone for 10 minutes to sift through their messages with the promise I'll give them free advice on how to solve their problems it's none of my business.
¯\_(ツ)_/¯