People are not concerned because it can, because as you say it needs to in order to operate if you opt in. The concerns implied are that: * You are automatica

People are not concerned because it can, because as you say it needs to in order to operate if you opt in. The concerns implied are that: * You are automatically opted in, or you are nagged to opt-in in a manner that makes it easy to accidentally do so, as is not uncommon with these things. * That the use of your data for training isn't just for you, it is also training any other models Google wishes to use it for. * That once they have started, opting out does nothing: your data is already theirs. Not that wasn't already anyway, control of how your stuff is used is apparently a right reserved only for corporations.