The students are investing and earning a good return no?...
It sounds to me, like you're demanding justification for something that benefits the vast majority of those involved... and I'm wondering why?
Let me pose the question: Is the current cost(on average) of a 4yr degree worth it? Are students being fleeced?
That question does not have a real answer, it's completely situational and dependent on the student, the school they go to, and their major.
But what we do know that having such a large number of young people in so much debt is a huge drag on the economy in general. People with a bunch of student loan debt are less likely to buy houses (and when they do it's at a later age), less likely to buy cars, more likely to live at home, less likely to get married or settle down, less likely to make any big purchases, more likely to have messed up credit, etc.