This argument can be extended downwards infinitely. You can argue against teaching addition and writing of any form with this mindset.
I also think this argument means that theoretically someone with a 6th grade education and a 12th grade education should have the same economic output, as they both know how to read and add/multiply numbers. In real life the reason someone drops out before/during high school is always extenuating life circumstances, so the outcomes are much worse for them. But in a world where that didn't happen, do you think the outcomes would be essentially identical?
There are too many confounding variables. But yes, I think that in a future world where kids who grow up in a stable family can choose to easily move between schooling and the real world (including work experience, travel, alternative education and just the occasional slacking off), you'll see improved outcomes for those who do these other things.
I also think this argument means that theoretically someone with a 6th grade education and a 12th grade education should have the same economic output, as they both know how to read and add/multiply numbers. In real life the reason someone drops out before/during high school is always extenuating life circumstances, so the outcomes are much worse for them. But in a world where that didn't happen, do you think the outcomes would be essentially identical?