I remember the creators specifically created Cartman to say things everyone wanted to say but couldn't. I don't think Cartman losing is propaganda, I think it's typical asshole loses in the end sort of deal, and besides he wins plenty as well getting away with murder in some cases. I also don't think they are trying to impose any other message other than trying to think of outrageous comedic scenarios.  Me, I think it's less propaganda and more they are running out of steam getting older making them less likely to want to take difficult positions.  They also indicated an unwillingness to do any episodes that circle around Trump stuff, which is too bad, because if they avoid the daily show 'herp derp orange cheato' routine then there's a gold mine of untapped comedy there.  But they aren't going to go there and so their stuff sucks now.