It simply states that they need to express somewhere else. Just like the Church's policy against demonstrations on Church property in downtown SLC. It is not preventing anyone from using freedom of speech, just that they can't practice it there, on private property.
I'm not saying I agree fully with the policy, but I think it is a stretch to say that BYU is infringing on anyone's religious freedoms. There is an issue in the US lately where people (not saying you are) think the right to excercise a freedom is a right to be sheltered from any and all consequences. You (again, meaning people, not you personally) may exercise your freedom of speech by walking up to my wife and calling her anyone of many deragotory terms. The result will be at least one fast punch in the mouth from me. Actions and consequences. To try and have one and legislate or otherwise do away with the other puts us on a very slippery slope as a society and nation. I will now get off the soap box.