I believe it is possible to ban them, with a combination of multinational regulation and technical coordination with ISPs. Not easy nor even likely.

ISPs could simply run honeypots that in real time sniff out who is running a blockchain node and block traffic to those IPs. These nodes must broadcast publicly to other nodes to even function, so they can't hide the fact that they are a blockchain node: they are forced to peer with whoever else is... peering in the same direction, pun intended.

I'd love to know what gaps in my knowledge invalidate the above thesis, though.