Meanwhile, even if you somehow had secure, irrevocable ownership of some kind of identifying name or number, websites could still cancel your account with them for any reason and keep you from logging in with that ID. They can use the ID to more easily share reputation information, similar to credit scores. Your ID could be put on a list, similar to what happens with ad blockers and lists of spammers.
By itself, ownership of a name or number doesn’t get you much. If you use Google to log in to a website, what it’s really providing is a minimal kind of reputation, sort of like how a captcha vouches that you’re probably not a bot. For an ID to be useful, there needs to be reputation attached, and that isn’t something you can do yourself; other people or entities need to vouch for you. It’s also not permanent. Good reputations can go bad if people decide they don’t like you anymore.
Instead of centralizing using a single ID, there’s a lot to be said for having having multiple identities (alts) for when you don’t need reputation and you don’t want what you’re doing to affect unrelated activities.