I'm pretty sure they've stated in interviews that their own personal beliefs are pretty much libretarian/conservative.
I'm not entirely sure.
They did an interview for a broadcaster here in the UK where they were talking about their intense dislike for their home state Senator - a beer heir in Colorado I think. Definitely a Republican.
Maybe it was just him they disliked?
And when Cartman, channeling Kenny's sould, goes into the abortion clinic and says, "I would like a living thing sucked out of me, please."