If they actually watched the episode, the first five minutes is nothing but poking fun at how liberals spout off at the mouth without doing any research. The only thing that I can think of that turned them off is when Lois came into the living room to announce that Rush would be at the mall and Brian said something along the lines of, “Rush Limbaugh set back the dialogue in this country by 100 years.”
Sure Seth McFarlane and the gang are unrepentant liberals, but they can poke fun at themselves once in a while to throw us a bone. I’m sure the same could be said about the South Park guys.
With South Park, if anything, they probably bash the left a tad more than the right. I once heard one their creators say they hate conservatives but really hate liberals.