However, poor work ethic as a mental shortcut plays into the just world viewpoint. Where lead poisoning contradicts it which is IMO why so many people think in terms of work ethic.
As can the effects of traumatic brain injury and chronic abuse or neglect.
I agree that what we call "bad work ethic" is just something that happens to people in that IQ range.
Now the problem is, what are we supposed to do with these people?
If I were to start a small business, I would probably like to avoid having such people work for me.
The only entities that can afford to hire these people are large corporations like Walmart and McDonalds, but because they are large and powerful, they also get to abuse these people.
A solution could be that the government offers help for people who struggle finding jobs. Training courses can help them finding (and most important, keeping) a job.
Some European countries already have courses like this and underemployment there seems lower than in the US. But crucially, free mental healthcare is an important part of this so that those who need help can get it.
I want to very clearly point out, that the fact that you agree doesn't in any remote way make the statement any more factual. This again is an unsubstantiated claim, presented with zero evidence.
I don't know why you assume the claim is unsubstantiated. I think it makes a lot of sense that people with lower IQs will have a lot of trouble in life.
Maybe it's not due to bad work ethic but merely due to them not having the cognitive ability to function properly in society in such a way that allows for the positive exchange of value.
I maintain that people with low IQ have this problem that makes it incredibly difficult for them to climb out of poverty, and I think this claim is very much substantiated, but I am not a scientist so I cannot back this up, but I have heard it on multiple occasions from people who I consider authorities on the subject.
I have pretty high IQ and a mediocre at best work ethic. I don't think these things are linked.
Is there a morally relevant distinction between mental illness and bad work ethic? There is a lot of research to suggest that things we associate with "bad work ethic" (e.g. lack of impulse control) appear extremely early in childhood development and aren't things people necessarily have much control over.
We need to stop moralizing things that people have no control over. We've realized this in a limited way--it is no longer acceptable to make fun of people with intellectual disabilities (IQ < 70). But there is still a weird doughnut hole were it is perfectly acceptable to make fun of people with 70 < IQ < 90. Your mental abilities are mostly an accident of birth, like having rich parents. There is no moral dimension to it.
There is a kernel of something I agree with in your post, though: social structures can add a lot of value in helping people who might not be that bright or might have problems with impulse control to lead productive lives. That's a major shortcoming of our current approaches to fighting poverty, which emphasize individualism.