See, that's precisely the problem. Cops don't act in anyone's interest, they act to enforce the law. Because they are bound by the law, they have a monopoly on the use of force. At least that's the theory. If you're the mafia and want someone to do the bone breaking for you, you can't hire a cop, you hire a thug. Such as this man.
Moreover, he was hired by the speaker, not by the library. He also didn't eject anyone, he choose to first intimidate, then injure someone. And he appeared thoroughly confused about what he was doing and on whose behalf. The library clearly isn't pressing charges for "resisting arrest", firstly because there was no attempted arrest that could have been resisted, and second because only the police state can press this particular kind of charge.
