> I disagree with this. It's clear in cases such as Facebook that data privacy is abused. Not only that, but users don't have much of an idea of exactly how their data is being used. In a P2P system powered by blockchain, I can set permissions for certain data my on-chain information to be accessible between different parties, whether that's a doctor or a friend on a social media platform. They can receive a hash an decode it locally to view whatever information I am granting them permission to view.

I think the OP is saying that if anyone has access to the raw data at any point, then they have some sort of ownership. And this is actually true in your example. A person owns their own data (age, email, etc.), and then gives it to Facebook. Someone might expect privacy from Facebook, but since Facebook now has access to that data, they have some sort of ownership of it. And what do they do with their ownership? They sell it :). If you give your hashed data to Facebook, and allow them to decode it and read it, then they can still sell the decoded data because they now have access to and some ownership of the data.