What is amazing about South Park is that it requires you to look beyond most basic, simple meaning and obvious dark humour. It is a caricature of stereotypical societies, revealing paradoxes, mocking people for their contradictory values and how strongly they stand for them, even though often they have no idea what do they really mean. Or how their expression of them is a negation of what these values stand for.
It is a perfect irony of how stupid the society might be, and in order to understand it, a certain level of maturity needs to be reached. The one that acknowledges that the cartoon is made to be as shocking, vulgar, grotesque, in order to depict this societal ridicule happening in every day life. That mockery is done on all levels possible, pushed to the absolute maximum limits. It is not only the plot and words used, but also the order of events and the way the characters are drawn. The show is made on purpose to look immature, exactly because it mocks immature society.
Stupid, offensive plot, vulgarity, prima facie lack of sense- all combined are the only way to create that strong grotesque, which is the only outlet trigger for appropriate mockery. Only this is substantial enough to actually show this whole, enormous, gone-too-far paradox happening in every day life. Each episode is made that way to be only a background for satire of real issues, those having gone too far into an unbelievable farce. Each episode is loaded with mockery of hypocrisy, stereotyping, inconsistency in beliefs, superficiality, and duplicity of people.
Staying in a rather flat reasoning and operating mostly on basic, simple level of meanings, will not allow to appreciate the parody that South Park is. You will of course be able to see it, acknowledge it, but not appreciate it.