In Rumsfeld v. FAIR (2006), the Court unanimously held that universities could be required to host military recruiters, even when the universities generally refused to host recruiters who discriminated based on (among other things) sexual orientation, and the military was indeed so discriminating. The Court also held that universities could even be required to include information about the military recruiters on the same terms as about other recruiters in the universities' own speech (e.g., e-mails or notices about recruiting events). To be sure, one could criticize the decision; consider, for instance, our own Dale Carpenter's article about it, Unanimously Wrong. But it's a precedent.
Of course, that still leaves the question of the scope of the precedent, and the extent to which it might bear on other debates (such as whether social media platforms may be required to be viewpoint-neutral in their decisions about which content to host). There is a lot to debate about that; but here I just wanted to note two points that strike me as particularly clear:
[1.] Rumsfeld upheld the Solomon Amendment, which imposed its obligations as a condition on government spending. Many people therefore assume that the precedent is limited to such conditions.