Using sociopathic/immoral characters in situations where they should reflect, but dont (or take the "wrong" stance) is a trope that goes back to Seinfeld. They are not deliberately/exclusively trying to make a value judgement. Usually it's social/political commentary specifically designed to shed light on how awful Americans can be to each other. It's (subjectively) funny because we have encountered milder forms of such people in real life, perhaps.

I agree that we are prude as a culture, just dont see how this is evidenced by the average sitcom. South Park in particular is a very strange example of a "prude" show.