You're talking about shows up to twenty years removed from Bakshi cartoons like Fritz the Cat or his eighties Mighty Mouse show. The Simpsons and such definitely popularized the medium, but it didn't create it.
>Shortly before that we had 'the Dungeons and Dragons' scares and it was the time of the violent video game and explicit music crackdowns.
There is always content that is slightly edgier that conservatives freak out over. Some outraged people didn't disrupt cable, cable embraced the cartoons and pushed things further with things like the creation of Adult Swim.