I think you're missing the idea of what makes something adult. Kenny can die in every episode of South Park. But while that may be violent, it isn't really adult. Now take some episodes of Ren and Stimpy for example. Someone might look at "Stimpy's Invention" and see no problem with it. But when you really look at it, it's the story about Ren painfull losing his free will and being forced to humiliate himself against his will for Stimpy, who thinks what he is doing is helping his friend to be happy. It's obvious Ren isn't happy, even when he's wearing the Happy Helmet and being forced to do things he'd otherwise never do.
It's not like the recent Spongebob episode where Squidward shocked himself and suddenly became genuinely nice. In "Stimpy's Invention" Ren, despite the smile on his face, is hating every second of what Stimpy is doing to him. He's being tortured by a simpleton who doesn't know better. Yes, the episode is very funny. But it's also very dark and it's very disturbing when you look at it carefully. That makes it much more adult than anything that's violent or derogatory for the sake of it. There's a reason Nick was a afraid of this one and for a while were dead set against airing it.