Petition Compulsory Charitable Donations For Super Rich

While Bill Gates does fantastic work with his billions, I feel it would benefit those in need immensely, and help battle inequality, if, instead of raising taxes on the rich, a compulsory charitable donataion of a certain percentage is made. A group of charities who are reputable, and represent a wide range of causes could be selected each year, to allow those who are donating, to think about what's important to them, and to what they would like to donate.

For example, the following bands could be debated and altered to find an agreeable solution

+£1,000,000 = 2.5% Donation
+£2,000,000 = 5% Donation
+£5,000,000 = 10% Donation
+£10,000,000 = 15% Donation
+£50,000,000 = 20% Donation

While we all would like to think we would donate large amounts as a matter of course, I think it would make giving money away a little more palatable to the super rich, if they didn't think money was being misused by goverment.