When was the last time you ever heard anyone say "Well, I'd like to go to college, but I can't afford it"?
Probably not in a few decades. The fact is, right now, anyone who wants to go to college usually can in some way, shape or form, even if they can't afford it. The consequences of doing so, on the other hand, are what caused a lot of the student loan issues we have today.
Free college for all won't increase attendance at universities. Most of them reject at least 40% of their applicants already, so there arguably isn't enough room at most of them even if there were an increase in prospective students. It will just shift the burden of educating the ones in college on someone else. Of course, we already have issues with employing the students we do graduate, especially in STEM fields, a vastly under-appreciated crisis.
Our broken college education system won't be solved by making it free.