Getting paid is fine and dandy. What's false is that "without a business model", nobody would be "insane enough" to write books (or programs).
The conflation between doing a thing and getting paid for doing a thing -- or even worse, claiming that without monetary compensation said thing wouldn't exist -- is annoying and misleading.
The best software is usually already the one written by volunteers.
You mean written by people who are not professional software developers? I highly doubt that. Can you provide some examples?
I meant the best software is written without expectation of remuneration.
My impression was that most successful open source projects (Linux, Mozilla etc) are driven by paid contributors.
I'm sure you can find some examples, but depending on your opinion on what the "best software" is, I doubt most of it is developed by people working for free.
Being paid for writing is great. It's just that the paid writing is not all writing - some people write simply to be read, without needing or wanting to be paid for it.
Writing code is different, because it's a means of self-expression only in small part.