The opppsite would be more logical. Selling data should be opt-in, in the absence of explicit consent no company should be able to sell data.
In case we agree on selling our data we should be able to set our price and get paid for sell, use and resale of data. It's crazy that those parasite companies get that for free.
But why would anyone opt-in to that? You could do what some site are doing put up a "Either pay us or opt-in to cookies and tracking". The problem is I don't think people fully understand how much tracking we're talking about.
Right now a Danish radio station is running a number of news stories about being able to track people who work for military intelligence or as police officers and prison guards. They do this using a free sample a data broker provided. Everyone act surprised when the journalists are able to show up at the home address of military personal or prison guards who have their home address protected/secret.
I don't think there's a safe way to opt-in to selling your data, because most people cannot comprehend how much data, what type or the ramifications.
In case we agree on selling our data we should be able to set our price and get paid for sell, use and resale of data. It's crazy that those parasite companies get that for free.