It really shouldn't be. We should have dedicated shelters for that.
Relying on libraries to be de facto homeless shelters is bad for everyone compared to the alternative of dedicated facilities. It's worse for homeless people, worse for the library and staff, and worse for patrons.
The problem is that we’ve wound up in an unhappy place due to the weird perverse incentives of ideology. Taking homeless people off the street, whether to a hospital or jail, costs a lot of money; so we lack something to do in a climate where a good chunk of the populace is rabidly against paying more money for anything.
I think you're right that people are against these things, but wrong about the reasons.
Taking homeless people to jail because they're homeless just seems stupid and pointless, not to mention harmful to the person going to jail.
Shelters have the issue where people don't want them near where they live (for often justifiable reasons) but obviously they have to go somewhere.
Unfortunately, the US is filled with people who are happy to make their own lives worse if it hurts people they don't like even more.
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