My favorite professor in university introduced me to South Park my first year because we were studying Seneca's Thyestes and the episode and the play had - ahem - similar endings.
The thing is, this professor is still one of the smartest people that I've ever met and he was utterly wrong when he said that South Park was nihilistic. Most South Park haters nowadays call it "apathetic" or they dismiss it as being scatological.
Sure, the scatology is part of the show's success. Yes, there are some episodes - including some of their best - that are just fun and don't have any kind of clear moral message.
Still, South Park is a show that delves deeply into complex moral issues and does take a stand. The Butt-Out episode is often regarded as apathetic in its lampooning of anti-smoking activists; but, it's not. It takes a moral stance on free choice and personal responsibility. Miss Teacher Bangs a Boy makes fun of the double standard of sexual abuse of minors based on gender and attractiveness of the abuser; but, it's making a moral point about it. Even Cartman Joins NAMBLA has a point to make at the end about the moral limits of tolerance and acceptance in regard to sexual preference.
Almost every episode that they've made has had some moral message.
So, why is it that people still think that the show is nihilistic or apathetic?
Well, I think that part of it is that younger millennials and people born later than that are living in a post-comedy world. We have a lot of people who will pretend that Hanna Gadsby and Samantha Bee are funny because it gives them political points. People also don't know that we're living in a world in which making a two part episode about a cartoon showing Muhammad in and of itself is a moral statement and really a braver act of activism than 99.9999% of people would ever make.
I also think that a lot of us think that mocking, not only the moral philosophy that sparked one's activism, but the tactics of the activism is a display of apathy. We virtue signal a lot. If I make fun of you going out and lighting dumpsters on fire for your cause, I must be a nihilist.
Finally, people don't get libertarian moral philosophy. South Park is unique in that the creators have alluded to their personal moral views leaning libertarian. Most of the time great libertarian art is made by non-libertarians who stumbled on it. So many of the moral messages are like the Butt-Out episode - "Yeah, this might be bad for you; but, you can do it and the people who are trying to take away your liberty are the real bad guys."
South Park might be the greatest show of which I'm aware that manages to proclaim the moral message that you can let people live their lives and that it's when you try to impose your ideal way of living on others that you become the bad guy.