The argument he’s making is coherent.

1) There are social, economic, and institutional norms surrounding sleep.

2) These norms are defined (or at least abided) by a majority group.

3) A minority of individuals can’t abide by these norms either due to physiological differences or necessity.

4) Some people benefit from the work that this minority does, and the minority is not adequately compensated in comparison to the benefits they generate.

Only because it uses words like "injustice" or "minorities".

It was my first impression as well, but if I get over my gag reflex and actually read the lines carefully, it seems the "injustice" basically means that people with different schedules are treated unfairly by society and the "minorities" are precisely those with different schedules.

To me it's the sum of that and using a term from hard science. But the whole article doesn't indeed look like the author is trying to do fake science.

Oh but as a person whose cognitive capabilities are highly dependent on the amount of sleep I get and as someone whose situation forced me to reduce my sleep hours at some point, I can fully relate. It's one of the problems you can be totally unaware of unless it touches you personally.