He didn't tell them to leave - he told them they are free to leave. Big difference. However, given the state of our PC universities, I'm doubtful MSU will continue to stand behind the good professor. Hopeful, but doubtful.
I just emailed the professor to show my support for his email, and asked him to notify me if MSU decides to take any action against him. I offered to try to drum up some support for him here on FR if needed, and invited him to take a look at this thread.