Im a bit confused what exactly means by banning end to end encryption. What would stop two parties from sending encrypted data across the wire and decrypt it on

Im a bit confused what exactly means by banning end to end encryption. What would stop two parties from sending encrypted data across the wire and decrypt it on the other end of it? How would they ban that? If one posts some gobbledygook encrypted text on a forum that only a specific recipient would have the key how would that be stopped?