I don’t have a problem with it showing that they are dumb, and I don’t think it’s done in ill-humor at all. I’m not coming from the politically correct perspective. I just think that plug-in-a-subject-and-tack-on-a-corny-punchline jokes just lose their inherent humor. Your Rosh Yeshiva joke is funny, though (I guess by the same token). 🙂
(Of course, this all has nothing to do with the fact that I still don’t get the joke.)