But to see the case as upholding a neutral policy that student groups should only receive funding if they allow all-comers is too simplistic. The pith of the issue turns around whether a public university's attempts to secure equality of access impede on a student group's free exercise of its beliefs (beliefs that by its very nature exclude other beliefs).
It is interesting to think about what an all-comers policy would mean, if taken to its logical conclusion. What would have happened had a political group, say Students United Against the Death Penalty, required students to be anti-death penalty in order to join? If Hastings enforced the "all-comers" policy, the anti-death penalty student group could be forced to admit a majority of students that support the death penalty. In effect, this could result in the silencing of the anti-death penalty students' expression, a serious First Amendment concern. For groups that are formed based on a shared group of beliefs, Alito astutely argued, "the consequence of an accept-all-comers policy is marginalization."
See the full ruling here.