It’s because the stigma is based on the “binge drinker” label and its implication of irresponsible levels of drinking, while the official definition of the label itself specifies a level of drinking that many would otherwise not deem an issue. eg. three restaurant-pour glasses of wine during a three course meal.
Isn't that up to those who hold the stigma?
I'd have a stigma against dog walkers who left their dog crap at the park, even if I found it was most dog walkers. (I don't think it is)