Buffet's a smart guy, and I think even a good guy, but his trust in authority is downright foolish.
I don't think Buffett is a "good guy," or even that great a businessman. His school of investing loves monopolies and other safe, protected entities. He's not really an entrepreneur or innovator at all; those are the people who really create wealth for the whole population in the long run.
As for why he doesn't just give his money to the IRS: Remember, this guy supported Kerry. He would probably be offended that some of his money would be spent on things like defense. By giving it to the Gates Foundation, he's assured that much, if not most, goes to liberal causes like abortion and environmentalism.
He may be the greatest stock picker that ever lived, but on economics and fiscal policy I'd just as soon listen to Barbra Streisand.