How would an optional, official parser be toxic?

[Dualgunner]

Well the "silently" excluding people cannot be reported. You can argue that people are doing it already but it is still true that having an official parser will "promote" more people to use it leading this scenario to occur more often.

"That which can be asserted without evidence can be dismissed without evidence." You can't just say "but it is still true that..." and expect that to suddenly become the truth.

I don't believe an official parser would lead to your proposed scenario at all. All the tools exist to do what you're afraid of today, and everybody who cares to use them that way already use them that way, because, as you said, it cannot be reported. So nothing would change on that front.