How about you decide what you do with your money, and Bill Gates and Marc Andreessen decide what they do with their money?
Exactly, WE. Thing is, there are millions of people that aren't included in that "we" and the benefits they get (i.e. saving lives) FAR outweights the benefits we'd get.
Donations like the one outlined in this article give me faith in humanity. It's nice to see us looking out for one another.
As for me, I strive to build business(es) so I can do the same, whether the most effective way to raise the standard of living for everyone is donating, building, or most likely both.