With free college, more students from wider backgrounds could affort it. That would increase supply in college graduates while decreasing supply in workers of skilled trades. Thus, the latter would get to demand higher incomes (while the former would see theirs decreased).
I don't know where I stand on that as it comes to education. Sure, a more educated populous is desirable but college no longer has a monopoly on higher education. The question to me is, do we need more of the type of graduates college is turning out? And if so, will subsidies further exacerbate the college tuition problem when college becomes "free"? It seems like distancing the payer and consumer leads to more unuseful consumption (one can look to healthcare or even college textbooks for examples)
Even today some people are making the argument that college grads can't find good jobs. Wouldn't more grads make the problem worse?
I think some of those college grads should find their way into skilled trades. The trades may lack some of the sizzle, but they definitely result in jobs that serve a purpose.