Why not just charge people to use the library?

Answer

Public libraries are public institutions. They are not reserved for those who can pay to use services. While pay-to-play works for private entities, the public library is part of the social infrastructure of a community, much like parks. Think of the parks as Boulder's backyard, and the library as Boulder's living room. Anyone in the community is welcomed to use the library, regardless of their economic status and ability. That's what makes libraries such an important part of weaving a community of all backgrounds, abilities, ages, and income levels together.