Only 35% of millenials have student loan debt:
http://www.gallup.com/businessjournal/188984/americans-big-d.... As you concede, if you are part of the one-third that doesn't go, it's probably because you couldn't get in. But to the extent the government should be spending public funds to help people,
those are the people who it should help first. Moreover, on a dollar basis, it's the people who have the most education that will likely have the most debt.
E.g. interest free student loans will help those who do a couple of semesters of community college a little bit, but will really help out the doctors, lawyers, etc. who take on six-figure debt.
This is part of a larger phenomenon of the American welfare system helping people who are already relatively better off. Own a million dollar house? You can deduct tens of thousands of dollars a year in mortgage interest! Have $200,000 in debt after going to a private college and getting a masters degree? The government will forgive it! Did you make a six figure income during your working years? Great, the government will not only give you the disproportionate share of social security benefits, it will pay out more than you put in!