Sure, but this specific part of the discussion was about it being a bad choice because "it’s treating the identifier like a password that is problematic", which

Sure, but this specific part of the discussion was about it being a bad choice because "it’s treating the identifier like a password that is problematic", which I objected to. I do agree that in many cases I would not want to use it as my web identity. (Those cases would also overlap pretty well with cases where I don't want to use my own email address, like when signing up for sites like this, reddit, Twitter and similar).