I think that Twitter (and by extension, Bluesky) is designed in such a way that it promotes hostility and division. You can't really have a good discussion when the format makes people limit their posting to super short messages; it means people just dump hot takes on each other and wind up shouting past each other. So in that sense I certainly would call it the platforms' fault. Twitter (and Bluesky/Mastodon) are toxic to our society and we would be far better off if they were never created.