Blockchains storing social data is good example. It's infringing by nature GDPR. A decentralised facebook-like social network on the blockchain is not possible anymore. Each node can be sue. It had happened with TOR exit nodes.
IANAL, but crypto-shredding seems to be a viable way to meet GDPR deletion requirements, making it possible to implement compliant blockchains. Of course you'd have to make the nodes comply, but that has nothing to do with blockchains.
But I still don't see the connection with the first amendment.
Yes, protects, it doesn't require them to. Facebook and its likes volunteering to destroy personal data on request really doesn't have anything to do with the first amendment at all.
Edit: come to think of it I'm not even sure it protects them, but again, it certainly doesn't require them to store or transmit anything.