Dude, I absolutely, can not believe you said this. It is a PUBLIC university. They don't own it; you and I do -- or at least those of us who live in Texas.
then they also won't be able to stop groups from displaying graphic photos of orgies, child sacrifice, mutilation, or anything else that is grotesque and offensive.
To some extent they won't -- you are right. But there are what's called time place and manner restrictions. Pictures of orgies can be restricted for reasons that have nothing to do with content. Photos of a sexual nature with no political purpose can be restricted. Child sacrifice and mutilation are illegal and I would suspect that photos of such (unless they are fake) are likewise illegal. So restriction of these photos can be done on a non-discriminatory basis.
sticking graphic photos in peoples faces without first giving them a choice is counterproductive.
I agree with you, but the first amendment has nothing to do with good taste.
But the school is in charge of administering it. For example, they can set hours of use.