FYI: check and change login passwords ASAP

[Aurikai]

Convenience and security are ever on opposite sides of a spectrum.

No they aren't, OAuth is easily fixes this, this isn't host based security, doubt you have a clue about IAM systems, so not surprised you would say something that naive.

Lots of banks and other institutions use that same technology to ease logins, even Office 365 does, even Blizzard, so you're just making excuses for SE spending poorly on security because you lack knowledge of how it works.