Philanthropy is a predictable outcome of an individual having met the basic needs of Maslow’s hierarchy. Consider how many more philanthropists would be created by returning this 30% back to individual discernment.
Emphasis on might.
Evidence suggests "a giant boat and some helicopters" is the more likely result.
Nobody wants to make sure the roof is shingled and doesn't leak but everybody leaves money for new stained glass windows or the organ that nobody knows how to play.
Philanthropy is anti-democratic; the people don't choose what is important to support, the wealthy few do. You can see that in the relatively poor public goods in the US, which has much lower taxes relative to peers.
I’d prefer not to rely on them.
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.
They sure have a pretty dim view of their fellow humans while paradoxically believing in the goodness of the gubberment.
One tiny correction to your post. While it's true that most income tax is in the region of 30%, the cumulative taxes would be of the order of 60% of what of what one could potentially earn. Cumulative taxes = income + payroll+ property taxes etc.
Also, your drop of it betrays a pretty fundamental lack of understanding. I stand by my statement that free market could never accomplish something like this. Eradicating a disease is nothing like a business making a pencil to sell.
So yes in a sense it is free market.
Especially disease eradication is beating nature in macrobiology and philantropic foundations are the optimal tool to do that.