I really dont see the need to mock an old, invalid man, Carnage. The Pope is not a ruler, he's a leader, and it's only for Catholics. From what I remember reading the Pope is selected by vatican officials (arch bishops and the like... I dont know the Catholic chain of command, sorry), though I'm not sure.

edit: and to note, I do find all the Family Guy jokes about the Pope funny, I just dont think it's all that classy to mock someone about their lack of health.