I certainly won't defend this episode, which indeed sounds vile and disgusting. But I'll say this for "South Park." Unlike most other shows, they don't single out Christianity for abuse, while honoring a host of sacred cows. They make fun of everyone. Which means that they're attacking the Church bothers me much less than it would coming from other quarters.
No doubt they enjoy nothing more than to poke fun at any and all religious groups. Perhaps, like the other posters to this thread, you missed the point. Here it is: They intentionally chose to air that segment on the Feast of the Immaculate Conception. Do they air their taunts against Islam during Ramadan? Or their taunts against the Jews on their High Holy Days?
Heck, what's the big deal! Mary is only the Mother of God. You go right ahead and defend Viacom. We catholics are being much too sensitive in defending Christ's mother.