Easy to say for a guy who built his wealth starting with an insurance company, which uses government regulation to make most of its money. Wealthy people put their money into the insurance company because life insurance payouts aren't taxable but estate taxes are. Then Buffet's insurance company gets to invest that money in low risk bonds to get basically free money before paying it out. This only exists because of insurance company lobbying - it only adds friction to the system and wastes time and resources, while insurance companies get rich extracting money from the system. This is how Buffet built much of his starting capital.
Then he keeps most of his earnings in the holdings company, and only occasionally pays capital gains. The guy's gamed huge loopholes in the U.S. tax system his whole life, and then has the audacity to say that "the rich" should pay more taxes? Physician, heal thyself.
Edit: Reply instead of downvoting? There's a bunch of not commonly known facts in this comment and it's getting some downs, a non-fact progressive viewpoint is getting some ups... that's got to be the most disappointing thing about HN lately, the trend towards up/downvoting based on politics and not content in a comment.