Library staff in my city are instructed not to do anything themselves about homeless. If there's a problem then they just call the police, who are equipped to handle it. Same as the city bus drivers are not going to enforce paying fares or making sure no riders are causing problems. They just pull over and call the police.
Their is no polite "middle ground" where a librarian can just confidently ask a disruptive homeless person to vacate the library. 9 times out of 10 that confrontation will escalate into a full blown incident. That's why the rule is always just to call the police.
The problem is not homeless peoples' reaction to the world. The problem is societies place for them.
Homeless people have always existed and likely always will. The problem is in the last 45 years we've built a brittle, zero slack society. We've optimized around a particular vision of middleclass life while steadily eliminating the margins that once allowed vulnerable people, those prone to homelessness, and increasingly young adults who just need a place to start from, to exist on the periphery without being put in constant crisis. We removed the pathways that allowed unstable people to find enough footing to maintain a place to live.
We've embraced an economic model that requires continual growth and ever more housing. We've destroyed via economics and regulation many of the housing options that once existed for the very poor such as boarding houses, residential hotels, man camps. Demanding that everyone fit into a middle class model at all stages in life is cruel. It's even crueler when we act surprised or judgmental toward people whom society has systematically left with nowhere to go.
In AI speak 'we optimized away the edge cases and then blamed the people who (always had/always will) lived in them'.
Imagine regulating that everyone must eat a meal individually prepared in an industrial kitchen, with a mandated recipe from the community (any missing ingredients and the meal can't be cooked) and approved by inspectors post cooking, and capped the total meal kitchen capacity. Not everyone would be able to afford that. For peoples' largest expense (housing) that is what we have done and today 50% of young adult Americans are living at home with parents because that is our current housing model. What happens to young adults that don't have parents to live with? In part, homelessness.