Love the idea...
I think the key disconnect here is that (AFAICT) you mean that we should treat stupidity as a mental illness in the idealized way we're trying to get everyone to treat the mentally ill (see this video: https://www.youtube.com/watch?v=0B5nfkaeplc)
We don't think of mental illness in such an accepting way yet. Maybe when we do, saying that stupidity is like mental illness is like physical illness is like something that deserves sympathy and help will make sense, but right now it sounds more like prejudice.
I see what you're saying and appreciate the insight, and will try to treat stupid people with sympathy instead of frustration, but think that this comparison doesn't quite work yet.
Prejudice is a good word for describing this post. The article really tries to make the point of "we need less stupid people" without drilling into the "why" and without considering a basic ethical viewpoint.
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.