Cartman is a fictional character - he’s not real and has no obligation to be a moral barometer or even be ideologically consistent. Matt and Trey will have him say and hold whatever viewpoints they think are funny - they’re not tacky ham fisted writers like a lot of modern audiences want who will only use him to be the opposite side of what they consider “correct”.

Like hippies aren’t suddenly great just because Cartman hates them. Family Guy’s righting isn’t suddenly deep because he thinks it’s shallow.