Well, though titty. Honestly, as a user, I don’t give a damn about the pains this can cause to developers. The amount of spam and unsolicited email crap this is gonna save me from is worth it 100% for the users. And as a developer, I honestly think that Third party sign ins are lazy solutions that empower data-hungry companies way more than they deserve. If your business model relies on people giving you their data or reselling their email or using it for unsolicited purposes (these are the only reasons you would be affected financially by a privacy-driven solution like SIWA) then your business model is bullshit. Suck it up.

EDIT: I really love the downvotes from developers that are perfectly aware this is how the things are.