Who the hell is making that argument like?
My argument has always been that their are certain jobs for which you need a degree to do them, not that you waould make a lot of money doing them.
FWIW, the money someone makes in a certain job is directly related to the market at the time, if their is a significant skills gaps in 'the trades' such as plumbing, then there will be a lot of money for those few select plumbers that do exist, over time however the market compensates and more plumbers are trianed, each trying to get in on the big money jobs, eventually forcing overheads such as wages down.