I agree it would be a dangerous precedent.

Thing is, though, every instance is not equally valid and legitimate: that's the reason for defederating from Threads.

Not sure what you mean by what Gmail and Microsoft did to email? Do you mean that they assume many unknown email origins are spam? Though Gmail's obviously attracted a lot of users, and I myself have moved off it now to paying for my email provider elsewhere, I was under the impression it's been quite good for email and for pushing secure email, and being good at anti-spam.