Well, on one hand, when people call others stupid or dumbass, it's more than just a derogatory term for having low intelligence. It's usually because they're angry at them for some other reason. So calling them stupid or dumbass is just a way to vent and you could say that calling it ableist is SJWing. On the other hand, the fact that these are the derogatory terms people use is revealing. It shows how lowly we think of people with low intelligence, even though our intelligence level presumably is completely out of our control. I don't know if people of low intelligence are especially hurt by the popular use of the terms "stupid" and "dumbass", I don't know if they associate those insults with their own social challenges. "Stupid" people, as in people who aren't profoundly challenged but do irritatingly stupid things, don't know they're stupid. And those who have profoundly low intelligence are probably not called "stupid" or "dumbass" very often because they exist in their own category.