IQ, education experience, the oppression of society, take your pick. Take an average programmer and an average backhoe operator. Give them both 120 hours to train at each other's jobs, monitored by an expert. Who will be a more suitable replacement for the other?
As a writer I like said- "you get upset when a toll booth operator takes a long time to count your change, but if they could count change, they'd be an engineer like you are."
Well, yes, software engineer takes a lot more than 120 hours of training to do that job.
But that's not to say if you gave the backhoe operator the same number of years experience learning programming as the software engineer, they wouldn't be just as good at software development.
Do you honestly believe that? They could be as good, but I would wager that they wouldn't on average. There is fair amount self sorting based on aptitudes.
Having known a large number of manual labor professionals my whole life, there is no difference between the good-at-heavy-equipment and the good-at-writing-a-crud-app crowd. You do get a wider variety of intellectual capacity on the blue collar side depending on the trade, but electricians, plumbers, heavy equipment operators, etc are all just as good at problem solving on average as any group of developers I know.
"Blue collar", "the trades" are just so broad in scope it's an unfair comparison. It becomes much easier when you look at specific manual labor professions and specific developer professions.
I totally agree that most good tradesmen are great problem solvers. I'm just not convinced that the types of problems and the aptitudes required to solve them are interchangeable.
As a writer I like said- "you get upset when a toll booth operator takes a long time to count your change, but if they could count change, they'd be an engineer like you are."