I don't think I have enough money or room to buy all the books I think are worth saving, and my list no doubt has some overlap with someone else's. If I did buy them, what if someone else wants to read them? If I lose it or it gets destroyed in some way, the chance it will be gone forever increases (assuming there are multiple copies). Entrusting the availability of knowledge to individuals like that sounds like a bad idea. There could be some kind of publicly funded organisation that can take care of a big collection of books, afford to keep them safe, and make them accessible to anyone.