You are right. If the trespasser had left when he was told to. Instead he chose to resist arrest and make a scene and attempt to stir a riot.
Now as far as dragging him out of the building, that would involve a risk to the officers. Many departments do not allow officers to drag suspects as it is likely to cause permanent back and spinal injuries to the officers. So what they needed to do was to make this idiot compliant enough to walk out on his own accord or unconscious enough to be carried out on a gurney.
Now to get down to the nitty gritty and answer the question I have not seen answered on this thread, how would you have made this particular idiot compliant in this particular case?
I'll answer your question. When the CSO arrived and told me that there was a student who refused to leave the library, I get my partner and go there. We have the CSO identify the student to us. One of us takes up a position near the door, but out of the way. The other moves AROUND behind him, not AT him, to provide cover in the event of a 'situation.'
We see that he's moving towards the door. There's no reason to approach him as he is complying with the commands given by the CSO. We keep an eye on him until he leaves, which should be in just a few short seconds at that point.
We go home.