A library is a place where one can sit down and enjoy the peace and quiet as they read a book or browse the internet on their computers. It does not always stay that way because there are occasionally rule breakers. These people may talk too loud, chew gum obnoxiously, or are just a general distraction.
In Universities, the library is a hot spot for doing homework and studying for difficult exams. Our nerdy librarian does not take kindly to rule breakers, and will promptly go from 0 to 100 when he spots a rule breaker. The library is his turf, and with his turf comes with his rules.