Seems kind of crazy. How much would it cost to cure AIDS or develop affordable treatments? He is treating many of the symptoms from which people suffer in the world. However, accelerating the advancement of science and medicine might be a better goal. There's probably lots of redundant medical research for example. Take some of the money and help fund a new era of open medical research.
Pretty sure he does that too through the Bill and Melinda Gates Foundation.
Quick look at the wiki page says that among many global health issues, the Foundation hands out hundreds of millions in grants for AIDS research on condition that findings be public. It's notably also involved in the development of Malaria vaccines like RTS,S, the first anti-parasitic vaccine in history, I believe.
