Personally,i feel unarmed(and probably untrained) security is a waste of money,i just dont see what good they do...
Well... without trying to be a jerk please consider this....
What good do they do? The ones in the library managed to enforce that illegal policy by hounding the folks open carrying until they left.
Yes, I know the folks who left had concluded their business at the library and then made the decision to leave.... but... it appeared to everyone else in that library that the security guards ran you out. So to the other patrons it ended up...
Security guards (and library anti gun policy) = 1
Open carry folks legally carrying guns = 0 ... zip... nada... made to look like fools.
The only reason a person dressed in an official looking uniform with an attitude of authority actually works on the general public is because, from infancy, we are trained to obey those who have authority over us. In most cases a security guard in a public place has exactly as much authority as my grandma has over you.... none, nada, zip. But, because we have been told to obey we generally do IF the person issuing orders appears to have the authority to do so (has a fancy uniform and an overbearing manner) ... whether they actually have any authority or not.
And faux police (security guards) rely on that obedience.... otherwise, if folks don't bow to the appearance of authority, all they can do is follow you around and act intimidating and overbearing hoping to scare you into doing what they told you to do. And no matter how long a person stays with security hovering around.. the minute they leave the illusion that the illegal policy is valid and the security guards have the authority to enforce that policy is burned into the minds of anyone watching as a truth. And that also goes for anyone who reads or hears about someone leaving after being told to by security because people will automatically think..... "The security guards must have been right or else why would the person leave?"
So ... what good do unarmed security guards do? They keep those in control.. in control.. because we let them.