Carlin was good at what he did but he absolutely did punch down, just not at a specific person. The overarching message for a lot of his comedy was “You know you’re all being screwed over and maybe you have a hard time doing anything about it, but you deserve it because you’re stupid.” It’s just such a popular sentiment to call everyone else in society stupid, while excluding oneself, that I guess few people notice those undertones and their implications.