Man, in this very thread the progression I'm bitching about happens with "There aren't any tankies!" comments.
"Leaves of three, leave it be" isn't a law, but it's quick advice. If you're out in the woods of Appalachia and see some ivy with three leaves, chances are it's Poison Ivy. "Generally posters claiming there aren't many tankies on the Fediverse are concern trolls" isn't a law, but it's quick advice. If, in the Fediverse, of all places, someone is not merely claiming to have personally not seen many tankies, but firmly saying (or implying through additional statements) that there aren't many tankies on here, they are generally a concern troll.
As for tankie apologists, I don't see why a tankie apologist should be regarded differently from a Nazi apologist, or any other fascist apologist. Ardent apologism by people not part of the in-group is a thing, and surprisingly common. Like atheists who praise Christians to high heaven (pun intended), or right-wing minorities playing "They're not that bad" games about the alt-right.