Much More Please

Columbia threatens to expel students occupying a building. 

This is classic bad parenting. Make the consequence severe and stick to it from the get go. Columbia keeps threatening to punish the trespassers with consequences and then hems and haws and so the trespassers just keep upping the ante like a child who throws fits to get his/her way.

The trespassers and their parents should be held financially liable for the costs to the University and other students for their trespass. Sic the bill collectors on them. Plus expulsion. Plus criminal charges. They'll move.