When people can't pay for higher education they do not go. We can take out loans from the government, but they are expensive 6.2% compounded while in school (unsubsidized). When people do not decide to go to school we create a positive externalities problem.
If more people could afford to go to school, then we would have a more educated workforce. We would be more productive and efficient. People would start more businesses and go greater things.
All of this would lead to a higher standard of living for everyone, a growing middle class, job creation, better decisions made when voting, more volunteers (more time to volunteer because they don't need to work all the time), more tax revenue from increased earns, and we could compete globally.