Libraries pay the publisher (who in pays the author in turn) and are limited to giving out one copy at a time (even electronic copies are often limited in this way). Piracy doesn't result in any money going to the artist.

Sure it does, presumably the original person that ripped their CD paid for it. Libraries don't pay the publisher "per checkout", they merely buy the books.

> Libraries don't pay the publisher "per checkout"

That depends: https://en.wikipedia.org/wiki/Public_Lending_Right

"A Public Lending Right (PLR) programme, is a programme intended to either compensate authors for the potential loss of sales from their works being available in public libraries [...] Canada, the United Kingdom, all the Scandinavian countries, Germany, Austria, Belgium, the Netherlands, Israel, Australia, and New Zealand currently have PLR programmes. [...] How amounts of payment are determined also varies from country to country. Some pay based on how many times a book has been taken out of a library, others use a simpler system of payment based simply on whether a library owns a book or not. [...] In the United Kingdom authors are paid on a per-loan basis calculated from a representative sample of libraries. The current rate is 7.82 pence per individual loan."

(I imagine that any occurrences of "authors are paid" should be replaced by "publishers are paid", but I don't know specifics.)

Libraries pay authors in most countries (such as the Public Lending Right payment in the UK).

Libraries only lend out the copies that they have purchased or access that they have subscribed to as previously mentioned. Libraries are a public good since they serve as a home for the local community and a benevolent institution for those who are very disadvantaged and might not even have access to the internet.

Book publishers have definitely tried to fight libraries before though, in the past couple hundred year history of libraries. Buying a book and then loaning it to _hundreds_ of people who would otherwise have bought it themselves was viewed as stealing from publisher/author profits. I think in some/many countries libraries still actually pay licensing fees to publishers? (similar to what/how radio stations do in the U.S.). The "first sale doctrine" that's part of copyright law in the U.S. says once you buy a book you have the right to loan that book out, give it away, resell it used, or even lease it out if you want -- but the first sale doctrine is particular to the US.

Music piracy groups mostly upload copies they have purchased or otherwise legally gained access to. Their torrents are a public good since they serve as a benevolent institution for those that are very disadvantaged and might not have the money to buy the content otherwise, allowing them to participate in modern culture.

For almost any kind of digital "piracy" you can make arguments that sound very similar to yours, because in the end libraries and piracy do something very similar: both buy content once and redistribute it for free. The only reason we treat libraries different is because of history and because libraries have a bunch of physical restrictions that seem silly in the digital world.