Society probably won't stop devaluing the less-intelligent any time soon. Because we praise the intelligent, we praise the gifted, we value the gifted and their works. Nobel Prize winners, leading Mathematicians, Scientists, Writers, great artists and musicians - all of those people are highly intelligent (well, maybe not what counts as a "great" artist or musician these days - I mean, Beethoven? Genius. Bach? Genius. Skrillex? Not so much of one). And we praise them for their intelligence. When not used sarcastically, the words "Genius" and "Clever" and "Smart" are universally accepted as compliments, and high compliments at that.
So it is not that surprising that we have exactly the opposite attitude towards those who are not "geniuses". "Stupid", "Idiot", "Dull", "Slow", "Moron", "Dumbass" - these are insults and everyone understands them to be insults. We don't value those who are not as intelligent. A genius can create a wonderful symphony or create technologies that make our lives easier, whereas someone who is intellectually impaired cannot do that. This has a powerful logic to it - if you are organizing a society or need to get a job done, who do you want to associate with? The intelligent scholar? Or the person who has difficulty counting past 10? As a society that depends on food and safety and technology, understandably (but not fairly) we look down on those who can't help us create technology, improve safety or grow food.
Let's be honest here - we look down on the less intelligent. It is not right to do that. It's not moral. It's not kind. It shouldn't be done - but it is. All our greatest achievements, all our greatest works, were created by the intelligent members of our society. In many ways, we DEFINE our species by our generally amazing intelligence. Homo Sapiens means "Wise Man" after all. Intelligence is so valued by our species that we incorporated into the name we gave ourselves.
I'm not sure if our species can truly ever treat the intellectually disabled with the respect they deserve. I admit that I myself have trouble doing it. I have to constantly remind myself not to view the less intelligent people as "less than human". It's a constant struggle, because I value the cognitive arts so highly. And when you value something so highly, it is very difficult to not associate negative feelings to its exact opposite. I praise the Nobel Prize Winning Scientist - they're the exemplars of our species in my opinion - and it's difficult to not then take that attitude and frown upon the poor person who really struggles with 10 + 10 = 20. I know I shouldn't look down on them. I know it's not their fault. I know they are still human and deserve rights.... but in the back of my mind... I can't help but shake the feeling that if a Nobel-Prize winning scientist's life was on the line, and a not-so-bright person's life was on the line as well, and I could only save one of them.... I... know which one I'm going to save each and every time.
And I hate myself for feeling that way.