Asymmetric cryptography is nice, and honestly, I think there are few (if any) technical reasons why they shouldn't be the default everywhere on the Internet — but let's not pretend that they somehow guarantee freedom of speech.
Twitter or Facebook could allow you to sign in with a keypair tomorrow, and they could still block your public key by its fingerprint. Your favorite Nostr relay could simply stop accepting messages from your pubkey tomorrow.
Freedom of speech is a social contract, not a technical one. It requires that everyone be at least willing to process your thoughts, no matter how offensive they might find them, without wanting to ban you just for uttering them.
