> Let the library know about specific incidents so they can handle it.

Library staff is not equipped to kick homeless people out for fear that it will cause a scene and possibly escalate to an aggressive situation. They will just call the police. So then the police will come and remove the person, but they will come back the next week, or maybe the next day. So then what happens? Call the police again? This time maybe they get charged with trespassing and put in jail? This goes on and on. The library is supposed to be a safe place but that also means that it is somewhat of a helpless place for staff and quiet citizens. And over time it slowly becomes more and more uncomfortable to the point that regular people just stop going.

It's nobody's "fault". It's just a tragedy of the circumstances.