but ultimately they're under contract from the city/county to provide library services? It's not like they can unilaterally add user charges. They still can if the city/county agrees, but that's still the case in the case of publicly run libraries.

I don’t have much faith in the privatization of public services like this—see private prisons, private schools, etc.

Private schools are far superior to public schools and often cost far less. Private prisons are almost a non issue - they're a minuscule amount. Take a look at what the California prison guard union does - advocating against criminal justice reform to maintain large # of inmates. I'm against private prisons, but don't let it crowd out the real issue which is public prisons.