I'm not sure where you're from, or what the composition of your social circle is, Lumifer—but I think you should find as many people as you can (or use whatever reasonable metric you have for determining a "normal person") and say: "Being stupid is a disease. The first step to destigmatizing this disease is to stop making fun of stupid people; I too am guilty of this," and then observe the reaction you get.
Personally, I'm baffled as to how you could think that this wouldn't engender a negative response from someone who's never been on LW before.
That being said, simply changing the theme from "anti-stupidity" to "pro-intelligence" would change the post dramatically.
I expect most of my social circle to agree that stupidity is a pathological condition ("disease" is too much associated with infections and contagion for me), albeit very widespread. I don't know why would you want to destigmatize is, though -- incentives matter.
It's great to make people more aware of bad mental habits and encourage better ones, as many people have done on LessWrong. The way we deal with weak thinking is, however, like how people dealt with depression before the development of effective anti-depressants:
The only "anti-stupidity drugs" we have are nootropics. But the nootropics we have weren't developed as nootropics. Piracetam was, I think, developed to treat seizures. L-DOPA was developed to treat Parkinson's. No one knows who started using ginkgo biloba or what they used it for; it was used to treat asthma 5000 years ago. Adderall derives from drugs used to keep soldiers awake in World War 2.
And none of them are very good against stupidity. AFAIK, to date, not one drug has been developed by understanding and targeting the causes of different types of stupidity. We have the tools to do this--we could, for instance, sequence a lot of peoples' DNA, give them all IQ tests, and do a genome-wide association study, as a start.
We don't research these things because society doesn't want to research them. People don't conceive of stupidity as a disease that can be cured. We need, somehow, to promote thinking of stupidity as a mental illness. As something drug companies could make billions of dollars off of.