I see absolutely nothing wrong with making fun of stupid people. And nerds. And a variety of ethnic groups. And pretty much everything.

That's an odd view. I'm presuming that you would see something wrong with, say, a popular kid in high school who made a habit of beating up disabled kids. But you see absolutely nothing wrong if the same person doesn't physically assault the kids but instead simply ridicules them publicly for being disabled? In both cases, it seems pretty clear that the bully is doing harm to the kids, although the nature of the harm differs.

Could you clarify what the morally relevant distinction is between these two situations, why causing one form of harm is bad and the other isn't? It wouldn't just be a distinction that makes the second option less bad than the first option; it would be a distinction that makes the second option not bad at all, if I take your words literally.

Or maybe I'm misinterpreting what you mean by "making fun"?

If you can filter out

They'll still answer the question,..they'll just answer it incorrectly and you'll throw noise into your data. OKC has many questions which are more direct proxies for intelligence.

I see absolutely nothing wrong

Which makes sense, since you're reactionary in your politics, and political correctness is seen as a lefty thing. I think this particular lefty value is fairly easy to defend though:

Humor functions to ease tensions when everyone is in on the joke. Insults directed at an out-group who is not laughing and is hurt raises inter-group tensions. Discouraging members of your in group from insulting members of out groups is just a special case of encouraging cooperation over defection - something which is both pragmatic, and to me. intrinsically moral.

TL:DR it's bad PR.

Exceptions exist. If you're giving some sort of constructive criticism to an out-group, and your criticism takes the form of mildly insulting humor, that's okay - because once again, you're using humor as an outlet for tension rather than a conduit for it.