I agree with the view of Benjamin Franklin in this regard, when he commented on his decision to decline a patent on a new type of efficient wood burning stove:

"Gov'r. Thomas was so pleas'd with the construction of this stove as described in (the pamphlet), that he offered to give me a patent for the sole vending of them for a term of years; but I declin'd it from a principle which has ever weighed on me on such occasions, viz., That, as we enjoy great advantages from the inventions of others, we should be glad of an opportunity to serve others by any invention of ours; and this we should do freely and generously."

- The autobiography of Benjamin Franklin

If I were to ever publish a book, I would encourage people to read it even if they couldn't afford to purchase a copy. Those who appreciate it enough to own a copy would later buy one, and that's good enough for me.