Should the Rich "Give Back" to Society?

The Gates example is flawed (he wouldn't have gotten rich without the existence of intellectual property), but the point is still well taken. Gates "gives back" so as not to get pies in his face. As soon as he started his charitable giving all the anti-Gates rhetoric disappeared. Why is that? The "counter-dominance instinct":
http://www.hedweb.com/bgcharlton/evolpsych.html
Why do we have an instinct for exploiting the rich, especially those without power? "Because that's where the money is." We have lots of instincts for using violence when it suits us. Sometimes they often come with justifications, like "He didn't really deserve that money. He got lucky. He took it from us. We need it more than him. He's greedy. He committed a crime." Thus the seeming compassion of the redistributionists is no different from the rationalization that goes on in the head of a simple thug. Gates is simply paying protection money.

I give this article only a 5 because it points out the obvious (to libertarians), without identifying root causes or offering solutions.