One of those skills is the ability to think critically about a variety of topics. My assumption is that University of Chicago believes that in order to develop those critical thinking skills, it is a REQUIREMENT to learn an environment with a free and open exchange of ideas.
Students that want the credential BUT they do not want to complete one of the requirements of that credential should reconsider whether the credential is right for them or perhaps find another university.
To use your grocery store/gallon of milk analogy, a more accurate version would be if I went to a grocery store and asked for a gallon of milk, but demanded that it be zero calories and made from tomatoes. The store owner would tell the customer that they can buy tomato juice or water, but there is nothing labeled as MILK which meets their requirements.