Sounds good, doesn't work.

Blockchain means you have to store all the shit on your computer. Somebody posts CP? Good luck explaining to le fbi man it's not yours.

You also need a lot of storage space. Average length of a tweet is 33 "characters". If we ignore metadata requirements and assume only people using English use it, this leaves us with 33 bytes per post. That's about 300 million posts for 10Gb of storage space. Not many people will be willing to dedicate more space than that for interacting with a platform. Again, this is without metadata, assuming it's only English (languages that don't use Latin take up more space), and without file upload. As a reference, 2 years ago Reddit stored around 30 billion comments.

One thing that might work is some sort of a "rolling" blockchain, the imageboard model where there can't be more than N posts at a time, with each new post (or thread) forcing deletion of the oldest one. Though that sort of defeats the purpose of blockchain, so it's probably better for it to simply be p2p, like a continuously updated torrent.

Then there's Tor. Not sure how familiar with computers you are, but connecting to a network such as Tor requires an entry node. You connect to this entry node, and it tells you "hey buddy, here's where you need to go from me!" and gives you an IP address. At this point you're good. As soon as you're through the entry node, you can use Tor as you wish, and there's very little your particular ISP/government can do to stop you other than cutting your internet access altogether or outright swatting you. But the very first connection, it requires you to be able to reach this entry node. And guess what, the IP address of this node is public. It has to be. Your ISP/government can just block all the entry nodes, if they desire so, and cut off your access to this network completely.

The second issue is not really solvable through tech. You basically need to build such a government (or other ruling body, such as a corporation) that values internet access freedom and privacy.

But this comes with problems. Now terrorists can plan their attacks with ease. Pedophiles can exchange their materials without fear. Human traffickers get record profits.

Though I personally think it's worth it. Bans don't stop terrorists or pedophiles or drug dealers or whatever. They just deter the 1% of lazy or dumb retards from engaging in these activities, while the other 99% always find a different way of communicating. But good luck explaining that to a mommy scared of her daughter being kidnapped, or a 9/11 survivor paranoid about terrorist attacks. They'll gladly give away all their rights if that means they get 1% safer.