When the blog author argues that "Warren Buffet should write a check" he is not oblivious to the fact that asking everyone in your tax bracket to pay more taxes generates more revenue than making a voluntary contribution. Rather, he is arguing that Warren Buffet feeling guilty about not paying enough taxes is not a good basis for rasiing taxes on everyone in that category.

Rather, taxes should be placed where they will do the least harm to the economy. Check out http://en.wikipedia.org/wiki/Optimal_tax. Ideally, taxes should be placed where they will not distort people's behavior. So, the relevant question is whether increasing taxes on capital gains will have a change investors behavior making the economy less efficient. Buffet says "My rich friends will invest no matter what!" But, he provides no evidence to support this. On the margin, some investments will not be worth it with a higher tax (as described by lionhearted). How big of a problem this is up for debate. But we shouldn't make tax decisions based on Buffet's anecdotal experience with rich friends.