(FORTUNE Magazine) – The rich folks who belong to a socially liberal group called Responsible Wealth want you to know they think it's wrong for the government to give special tax relief to individuals like themselves. So 76 of these well-off, well-meaning people have pledged to donate to charity their newest capital gains tax break--the difference between the 28% rate they used to pay and the 20% they now pay--for a total $1.5 million this year.

News outlets across the nation eagerly publicized this dog-bites-man tale. FORTUNE, however, decided to ask a snarky question: Are these do-gooders as self-sacrificing as they seem? The answer from tax experts is "not really."

Take Bob Burnett. The former VP of engineering at Cisco Systems, like most of his fellow protesters, doesn't shun every tax break. He's taking a charitable deduction for the $128,000 in capital gains tax savings he's giving away this year, stemming from his sale of some 22,000 shares of Cisco, which netted him a gain of $1.6 million. By taking this deduction, Burnett will actually be out of pocket only $77,312 at his 39.6% tax rate (since $77,312 is 60.4% of $128,000). Of course, the charities on the receiving end--several nonprofit organizations, including some that help children--won't care: They are still getting the full $128,000.

What's more, a faulty assumption underlies the entire exercise. Pledgers donate to charity the difference between the current long-term capital gains rate of 20% and the previous rate of 28%. But they don't have to take the cap gains tax break (or any deduction, for that matter) at all. They can voluntarily pay tax on their capital gains at the ordinary income-tax rate, which for those in the top bracket is 39.6%. So one could argue that Burnett's true benefit from the cap gains preference isn't the $128,000 he owns up to (the difference between $320,000, or 20% of his capital gain, and $448,000, or 28%). He actually saved about $313,600 (the difference between $320,000 and $633,600, or 39.6%).

Had Burnett donated his Cisco stock itself to charity rather than the gain from selling it, he wouldn't have had to pay any tax. He also could have written off the full value of the stock as a charitable donation (within certain income limits). If he did that, though, he would be merely a philanthropist, not a tax protester. And how much buzz would that create?

--Jeffrey H. Birnbaum