I often rant against idiots, and would like to explain that I'm not usually referring to those who, through no choice of their own, have insufficient reasoning ability to perform the usual round of everyday tasks without requiring extensive assistance from those around them, but those who take advantage of the fact that if they don't do something essential, someone more responsible will eventually do it for them.
These people are, on the whole, comfortable as they are -- after all, other people are doing the work -- and hence are reluctant to change -- after all, that would involve making an effort which could benefit someone other than themselves..
They may also be proud of what they are, and pathetically abuse those more capable or more diligent than themselves with things along the lines of ``Who do you think you are?'' or ``Think yourselves too good for the likes of us, do you?'' -- see C. S. Lewis' ``Screwtape proposes a toast'' for a good description of these people.
The term ``learning disability'' is often used to describe the condition in which someone has much less reasoning ability than is required for a normal level of independence -- I get the impression that the term is chosen to shy away from the fact that it is reasoning ability, not just learning ability, that is impaired. But, interestingly, ancient wisdom such as The book of Proverbs points out that there are none so stupid as those who will not learn.