Why force people to be vaccinated?

Many universities are requiring COVID-19 vaccinations for returning students.  Other organizations have the same kind of requirement.

 Why should people be forced to be vaccinated against COVID-19.

Vaccinated people are not at appreciable risk from unvaccinated people.  There is little reason for them to have a say over unvaccinated people.

Unvaccinated people prefer taking the COVID-19 risk to being vaccinated.

There is a tradeoff between freedom and the cost to others of your behavior.  In this case, the tradeoff appears to favor freedom not to be vaccinated.