Let the market forces decide. Eventually people will realise college doesn't work and will stop going there. Seriously problem is that too many people think they are smart and can benefit from a degree, when most can't. If 10% top graders go to college from school as it was in the boomers' era, ROI of higher education will be enormous (as there won't be an oversupply of useless graduates), and costs will be low (as low demand always reduces prices).
We shouldn't punish people who take the money because people are willing to pay it. Who's fault it is that they are dumb? Do we see much say, annoying advertisement to the tune of "go study X with us, you'll be rich and women will love you"? No. People are doing it because they are dumb. If we try to build a system that prevents smart people from taking money put on the table by dumb people, we will make the whole system dumber by incentivising dumbness.