[rhn_mk1]

That's an impediment, yes, but it's not a barrier. There's nothing preventing billionaires from putting their money into causes which are not charitable. There's only a disincentive in the form of lowered efficiency.

[s1artibartfast]

Sure, but now you are arguing that the rich shouldn't be able to spend money as they choose, and not against deductible philanthropy.

That is a different beast entirely.