Also, why assume that the trade guy wouldn't continue his education later and move into a white collar position, with lots of experience and possibly no debt? Instead of leaving college at 23 with a 2.8 gpa and a comm or psych degree, which we all know if barely better than no degree at all, a guy could be working full time at 20-21, make an average of 45k in his 20s, possibly get some reimbursed classes for construction management, engineering, many related degrees. So he's 30 instead of 23 when he gets his degree, with 9 years of work experience, knowledge of a field, contacts in that field, and less debt probably.
I just feel that about 20% of my buddies at my 4 year lib arts private school were completely wasting their time. It's not that they weren't smart enough to so college (we all know that outside if some STEM degrees, college is not that tough). It's that they weren't mature enough, weren't serious enough, weren't driven enough. They were 18-19. Spending 30k a year because mom, dad, everyone told them they should. Most of those guys dropped out between end of first and beginning of third year.