Allow me to remind you that people do not need badges to get into buildings. There are not guards at the door. There are a large number of public buildings to which doors are not even locked. There is not a fence around the campus, and there are not guard dogs patrolling the perimeter. The university is an open, somewhat unregulated place whose purpose is the creation and exchange of ideas.
Freedom is paramount.
Not just academic freedom, but physical freedom. People must be able to walk where they need to walk, to see what they need to see, to touch what they need to touch. Obviously some parts of the university need to be protected from some people, so some of the doors will be locked. But the Stanford campus has 200 buildings on it, and I am free to walk into almost any of them any time that I want. I notice that there is a teenager taking books out of the building and putting them in his car, and that after I watch for a short while, I conclude that he is not the owner of the books.