IMO the problem with Facebook is the private data they vacuum. If you publicly post the data on an open network, I see no problem with them taking it.

In practical terms, Facebook is actually quite tame compared to any other malicious actor who can get the same data. FB just wants it for ads and processes it in aggregate (most is never seen by a human), while other malicious actors might actually target you personally.

The main issue is that you shouldn't post anything on a public, unauthenticated network that you wouldn't want random, potentially-hostile actors to see.

This feels like another instance of seeking a technical solution to a legal problem

People seek mitigations to problems when solutions are not available.