This may be the cynic in me talking, but I've had enough trouble getting a group of six people to decide where to eat that I'm highly skeptical of the masses endowing libraries.
I'm not saying it *couldn't* happen. I am saying there is a certain simplicity to the process of a captain of industry just deciding to devote a huge chunk of their fortune to philanthropy that you don't get out of a committee (for good or ill).
(And for the record, I'm still very much on team if-you-make-a-billion-dollars-your-marginal-tax-rate-should-go-to-100%, while at the same time not having *deep* faith that the money the government would get their hands on would go to a library and not, say, police drones).