For most of our recent history, how to pay for college was one of the first big economic lessons a young adult faced. They learned how to balance debt and priorities, work and go to school, apply for scholarships, and more. This was a great lesson in managing large scale finances.
Now, students are going into college racking up as much debt as possible with the mindset they don't have to pay for it and their contract on the debt means nothing. They are learning the exact opposite lesson- they don't have to think about the future, their name on a contract line doesn't mean anything if they can just be loud enough, that debt is something to be negotiated after the fact, not avoided.
Not only are these Bernie Sanders type proposals ripping this opportunity from students, it is also giving them a very unhealthy start to adulthood in regards to understanding how finances and contracts work.