If directed at another poster in GQ, who did not self-identify as a racist, I would regard it as a personal insult and probably issue at least a moderator note to dial it back. Someone who made a habit of it would probably receive a warning.
Identification of non-posters as racists would probably be allowed. An allegation that a particular statement or point of view was racist might be allowed depending on the context of the discussion,
To understand your disagreement, I think we need some links to specific instances that you have observed. Where, exactly, have you seen this? Also, if a post accusing another poster of being a racist wasn’t reported, it’s entirely possible that a moderator could have posted in the thread without being aware of it.