Do you have any concrete examples of such industries with universal tight profit margins?
Well, here is a dataset with operating and net margins by industry:
http://people.stern.nyu.edu/adamodar/New_Home_Page/datafile/margin.html
I’ll do the heavy lifting for you and download it in excel and sort to find those industries with operating margins under 5%:
Retail (General)
Steel
Healthcare Support Services
Engineering/Construction
Retail (Online)
Food Wholesalers
Retail (Grocery and Food)
Telecom (Wireless)
Auto & Truck
Coal & Related Energy
Brokerage & Investment Banking
Bank (Money Center)
Banks (Regional)
Nothing too important I guess. Just some inefficient businesses we will all be better off without.