I wonder if you know of situations in which a project maintainer would not review/accept a patch because of the background of the patch author.

It would require them to specifically search for information about the author, which I can’t imagine anyone doing. That, unlike posting something on twitter, would indeed be indecent.

I’ve seen many instances of project contributors being flamed because of their “bad” behavior on twitter or elsewhere, but have not seen anyone accused not judging a specific contribution based on its merit.