People of all major faiths should take offense at this episode - Catholics and other Christians, because it offends the Mother of God; Jews, because Maryam was a Jew and Muslims, because they also treasure Mary.
The "Family Guy" show has done a spoof of the Pope, and that is a Fox program. How many Catholics complained about that?
"South Park" is all about being rude, vulgar, offensive, and blasphemous. That kind of humor walks a fine line. Sometimes it is hilariously funny, but when the joke fails it becomes offensive.
Personally, I thought the Monty Python "Life of Brian" movie was far more offensive than this "South Park" episode.
I'm a Protestant, so while I'm disgusted at any slander of the Virgin Mary, my reaction is not the same as it would be if I were a Catholic.
Those who slander the Virgin Mary are not interested in offending me (or Jews or Muslims) but they are intent of sticking a finger in the eye of the Roman Catholic Church.
I suspect the writers of this episode dislike the Catholic Church and enjoy the discomfort their work inflicts on Catholics.