So, if students wanted to invite pro-NAMBLA or pro-illegal drug groups in to speak at the schools after-hours, the school could not stop them?
Fair question, Modernman. I am not entirely sure.
What I am reasonably clear about, because of a number of court cases specifically involving religious groups, is that religious groups cannot be denied access solely based on the fact that their purpose or content is religious in nature. They can be denied access for other reasons, but those reasons must be applied fairly and evenly to all groups.
Perhaps religious groups enjoy extra protection thanks to the First Amendment that pro-NAMBLA and pro-drug groups do not have.
Also, perhaps groups advocating illegal activity can be excluded without recoures.