I think free speech is the way to go. A professor should teach as he wishes. Students should be free to not take that class and fulfill that requirement, if it is a requirement, in other ways.
As he wishes?? Not if it amounts to indoctrination.
There lies the problem. I agree that free speech is the way to go. But state university classrooms are often "captive audiences" filled with students who are required to take the class to graduate, and risk a GPA killing grade if they dare to challenge the professor's free speech with their own free speech.