Their biggest point, that it's already subsidized and the cost to the student is nominal, might be flipped: If they're already covering 93% of the cost, is capturing that additional 7% so valuable? Are they spending resources sorting out who has to pay the 7% and who can prove they're poor enough to trim that down even more? Or any other resources involved in extracting that 7%?
If, as the author suggests, if the nominal income requirement has a screening side effect, would they be better off directly screening for whatever that is?
I don't pretend to know the answer, but it's an interesting question.
"If fighting is sure to result in victory, then you must fight! Sun Tzu said that, and I'd say he knows a little bit more about fighting than you do, pal, because he invented it, and then he perfected it so that no living man could best him in the ring of honor. Then, he used his fight money to buy two of every animal on earth, and then he herded them onto a boat, and then he beat the crap out of every single one. And from that day forward any time a bunch of animals are together in one place it's called a zoo! (Beat) Unless it's a farm!"