"Looking worse than Cinderella after midnight..."
I used to go to the library pretty frequently, back in the days before I returned to school and before we had internet access at home. The public library attracts a pretty strange mix of people. These days, one of the major populations at any public library in a city of any reasonable size is, of course, the homeless. It's warm in the winter, air conditioned in the summer, there's public bathrooms, and if they're lucky, they can even maybe find a quiet corner and take a nap without being hassled by the security guards.
Here is a fascinating piece by the former assistant director of the Salt Lake City library about the new role librarians find themselves playing in the ongoing linked problems of homelessness and untreated mental illness. Suddenly, people with no training are expected to be social workers, paramedics, police, and still help people find a biography of Henry Clay or "that one book by that guy who wrote the other one a few years ago."
As fervently as we might wish this problem would just go away, it won't. The way we treat those who cannot take care of themselves says a lot about our society. And expecting somebody who's got a Bachelor's degree in English Lit and a Master's in Library Science to handle it when an unmedicated schizophrenic starts screaming and threatening people just because she's there is less than a bad solution, it's no solution at all.