This isn't about freedom of speech, you idiot. The students were expelled over conduct. When you sing songs about lynching "N's it creates a hostile environment, and those students were in violation of school policy, for which they signed a contract.
And the stretch begins. What they did was speech. Its speech a lot of people (including some of their defenders) do not like. It was not done in front of people who might have been offended, it was not directed at any person in particular, and it was not endorsed by anyone in any position of power (which is usually needed to create a "hostile environment"
Even the ACLU agrees that the University probably went too far.
ACLU of Oklahoma Statement in Response to the University of Oklahoma s Announcement of VP of Diversity Position American Civil Liberties Union of Oklahoma
Bring it on! Obviously, any lawsuit is going to involve extensive discovery, which is likely to determine when the offensive songs were written, who wrote them, how long they have been a part of life at SAE, and lead to significant detrimental publicity for both the local chapter and its members and alumni, and also for the national fraternity.
Let the SAE make a public spectacle of themselves, demanding the right to chant about lynching "N's" in trees!
The UCLA also states that "the University of Oklahoma has an obligation to protect all of its students from a hostile learning environment that impedes their educational opportunities."
And that's exactly what OU is doing.