I'm not sure how your argument actually contradicts the argument of the article. State support for public universities declined while state issued loans to students increased. Both would seem to facilitate higher priced private universities and work together - if you just have student loans, student might still prefer lower priced public universities. If you just defund public universities without the massive expansion of student loans, many student might be not be able to attend university.

Also, I get the figure of inflation-adjust college education cost doubling over thirty years. You can spin that as "only slightly beating the cost of living" but education is a major part of society's expenditure of resources and so such a doubling, over a longish time is still majorly important.