> Consider how many more philanthropists would be created by returning this 30% back to individual discernment.

Many, many fewer than you assume.

Libertarians like to make lots of good-sounding promises to justify their favored radical policy, but it's bullshit and the promises don't pan out when tested [1]. By that point, the libertarian has gotten what he wanted and moved on.

[1] Or their policy was already tried and already failed, e.g. https://news.ycombinator.com/item?id=46876387, leading to reforms to fix the problems that they're now mad about and want to undo.