I cannot stand the apps and systems that, when blocking, just totally purge and puff the conversion out of existence, not just for the block-er, but the block-ed. Both sides have the right to their memories! Maybe Y poured their soul there, and they want to continue having access to those moments; X does not get to have ultimate control over that.
If X or Y want to block, then the blocking action should just lock and prevent further replies. (And there's definitely way more nuance possible here that I will be getting into here.)
The "nuclear" version would be to hide the blocker's part of conversation of which I also extremely disagree: everyone needs to learn, experience consequences, and evervigilantly practice to stand behind one's words — but those should always be remarkated with he fact that the stances, feelings, opinions expressed then should be considered ephemeral in an ever-evolving state, and not etched in stone. (And even add a short revision note tag function: "This is no longer considered valid, more info here / ask me more".
And while I have presented this example here as a private conversation between two people, my thoughts on the group conversations are very much aligned to these.
However, I am mainly of the opinion that block as a function should he reserved for the gravest of offences, and that people should (continue to) learn to settle their differences of opinion peacefully and as amicably as possible. Blocking willy-nilly does the exact opposite of it, and just builds the ever-more-impenetrable echo chamber(s) of samethink.