People have articulated all kinds of actual harms, including two possibilities in the OP, but frankly they're irrelevant.
We know what Meta's goals are, and we know they have absolutely no moral standards whatsoever. Exactly how they try to accomplish those goals doesn't matter. We shouldn't give them the opportunity to try anything.
We should be scared of Meta, and we should keep them as far away as possible. Anything else is reckless and stupid at best.