Re: The problem with small-scale private philanthropy by the wealthiest is that it achieves little
"How on earth is it immoral?"
It's immoral because you have decided that your causes are more important than what society has decided should be paid for. So it's deeply arrogant and egotistical.
Making a (gift-aided) donation to the RSPCA, which is overfunded, takes money away from schools and hospitals, which are underfunded.