> it still limits a lot of types of uses and sharing (any with externalities sufficient they might get caught)

I don't understand what you mean

> For example, if personal data was being sold by a data broker and being used by hedge funds to trade

It's pretty easy to buy data from data brokers. I routinely get spam on many channels. I assume that my personal data is being commercialized often. Don't you think that already happens frequently?

I honestly would not put on a textbox on the internet anything I don't assume is becoming public information.

A few months ago some guy found discarded storage devices full of medical data for sale in Belgium. No data that is recorded on media you do not control is safe.