the data that is physically within your system is yours alone.

Actually, ALL the data Google has on you is yours. Google do not own the data, neither do reddit, Facebook or anyone else. They merely have a licence.

Personally I think even that is illegal. Contracts require consideration, you exchange x for y, then you have details in the terms and conditions. This is like "come in for free!" and then everything is in the terms and conditions. If you look at insurance, they're required to have a key facts page to bring to the front the main points from the terms in plain English. The cookie splash screen doesn't really do this, as it obfuscates just how much data they collect, and is for the most part unenforceable as you can't see what data they hold. Furthermore, the data they collect isn't proportional to your use of the website.

The whole thing flies in the face of the core principles of contract law under which all trading is done. They tell us our data has no value and it isn't worth the hassle of us getting paid, yet they use that data to become some of the wealthiest businesses in the world. We might not know how to make use of that data, and you'll need a lot of other data to build something to sell, but a manufacturer of nuts and bolts doesn't know how to build a car - yet they still get paid for a portion of the value derived from their product through others' work, as most of the value comes from what you can do with it. We're all being robbed, every single one of us, including politicians and lawmakers.