These people can't be helped. Meanwhile, you are harming functioning healthy people and destroying any public space at great cost to everyone paying the bill. We are all sick of it.
No, I don't think they can be helped; additionally, I don't accept that functioning productive people have to sacrifice their comfort or well being to accommodate these people's problems.
I don't think they can be helped, but certainly letting them mill about in public libraries accomplishes what exactly? Yes, I write them off because I am a realist, not a utopian, and I write them off because on balance they cause so many problems for normal people.
It is not worth destroying nice places, cities, libraries, streets for pie in the sky morality that presumes mental illness to this degree or drug abuse can be overcome, or that it is worth all of the mess, harassment, violence, filth, and degradation that we all see everywhere waiting around for this supposed solution that never comes. It's not working.
It might be interesting to actually try to help these people before writing them off entirely like that.