And that's the article's point: college is so damn expensive now, almost everyone has to take on debt to pay tuition. The undergrad experience is badass, but it's also fraught with problems:
-- Students are asked to choose a major (and thus, by implication, a career) before they turn 21. If they choose incorrectly and need a different degree, the costs are astronomical.
-- Non-engineering classes are completely bunk until about the third year. Before then it's mainly "weed-out" courses which teach students little or overload them with work.
-- The cheapest (public) schools also have the largest classrooms. You pay less in tuition, but quality of education suffers.
We ask students to decide on a career during a transitional phase in their lives, in an economy where no one works in the same field for more than a decade, and then charge them $50k in the process? That's just unfair.
We also know that the gap in income between those with a higher education and those without is increasing significantly.
1 + 1 = 2
There's an unaccounted for correlation between the accessibility of higher education and general life opportunities.
My point was about the widening of the income gap, the correlation you speak of doesn't explain the widening of the gap.