That covers exporting one user’s data at one point in time, sure. But you can’t read all public events without significant work on a scraper, and you certainly can’t contribute without going through Facebook’s servers. Of course you’re not forced to use Facebook, but in order to use Facebook you must go through their computer systems on their terms.
But the goal of most people isn't to use Facebook; it's to keep in contact with their friends. Scraping just the things they care about is fairly easy; scraping what Facebook chooses to put in front of their eyeballs when they're using an account (in practice, what they'd see if they were using Facebook) is really quite easy.
Then you can just reply to Facebook messages on something other than Facebook. That'll annoy your friends a bit, but that's the cost of them still using Facebook.
The problem with Facebook is not that it's hard to get your data off. It's not, really. The problem is that you have to be a programmer to do so; and blockchain stuff doesn't fix that problem.
