The chairman of Berkshire Hathaway, Warren Buffett, will host a presidential campaign fundraiser for Senator Clinton in New York City later this month, according to a report by Bloomberg News, and it is a moment to ponder a missed opportunity. Mrs. Clinton, after all, had a brief and promising turn as a capitalist, turning $1,000 into nearly $100,000 in 1978 and 1979 by trading cattle futures based on her own research and reading of the Wall Street Journal, and serving from 1986 to 1992 on the board of directors of one of America’s most successful companies, Wal-Mart. Mr. Buffett is one of the richest men in America, a phenomenally successful investor who bills his company’s annual meeting in Omaha as the “Woodstock of capitalism.”

The tragedy is that, under the tax plan Mrs. Clinton rolled out last week, she’d be raising income taxes on all filers earning $200,000 a year or more. That won’t have much effect on Mr. Buffett, who has managed to accumulate a vast fortune for himself and his shareholders without paying much in the way of personal income tax. We don’t begrudge him that fortune an iota. But raising taxes will make it more difficult for many Americans whose income comes primarily from earning salaries as opposed to owning businesses to accumulate their own, smaller-scale fortunes.

Mrs. Clinton has offered her own philosophical justifications for tax increases over the years. Mayor Giuliani pointed out last week in San Francisco that, in 2004, Mrs. Clinton explained, “We’re going to take things away from you on behalf of the common good.” In New Hampshire, she decried “robber barons” and spoke of trying to create a culture of “shared prosperity.”

Sorry, but it’s hard for us to see a two-income family earning $200,000 a year in Manhattan as “robber barons” in an era when tuition, room, and board at an Ivy League college is $43,000 a year, when the average rent for a two-bedroom apartment in Manhattan is more than $4,000, and when even some parking spots in Manhattan are renting for more than $1,000 a month. Mrs. Clinton’s planned increase in the income taxes of a group of earners that already pays 49.98% of the income taxes even though it is but 5% or so of the population, combined with a vast expansion of the federal role in the health care system, would be a step back, away from capitalism.

As Mr. Buffett’s own example of giving away his fortune through the Bill and Melinda Gates Foundation shows, sharing prosperity for the “common good” is possible without the government taking things away. Sometimes rich people, even when taxes are low, give a lot of money away. It’s not only Buffett — we think of Berkshire Hathaway shareholders who have enriched New York City with their philanthropy. Donald and Mildred Othmer left $340 million total to the Brooklyn Historical Society, Long Island College Hospital, and Polytechnic University in Brooklyn, among other causes. Myer Kripke, an Omaha rabbi who invested in Berkshire Hathaway, reportedly gave $15 million to the Jewish Theological Seminary in Manhattan.

The academic research on the effects of raising taxes is clear enough that economics professors can describe it in their own jargon. A Harvard University economist, Greg Mankiw, who maintains gregmankiw.blogspot.com, cited a paper by Nobel laureate Joseph Stiglitz, a professor at Columbia, who writes that “Pareto efficient taxation requires that the marginal tax rate on the most able individual should be negative.” Comments offered on the blog post described it in more concrete, personal terms — from the decision of a second earner in a household earning $250,000 a year to stay home with the children instead of working because the phase outs of so many tax deductions at that level don’t make it worthwhile, to the decision of a doctor or dentist to spend more time on the golf course and see fewer patients. Or, as one commenter put it, “If income was taxed at 100% on Monday and 0% on Tuesday, which day would you work harder?”

While it’s nifty to see bloggers and economists defending capitalism, and while Republican presidential candidates leaped to attack Mrs. Clinton’s proposed tax increase, what tends to disappoint us is the shortage of leading capitalists who are ready to defend capitalism. There are a few out there — we think of Charles Koch, Boone Pickens, Richard DeVos, Steve Forbes. Mitt Romney has potential, as does Michael Bloomberg, though of all Mr. Bloomberg ‘s strengths, which are many, we wouldn’t put an ability to publicly articulate the virtues of free-market capitalism particularly high on the list. The missed opportunity is for Mr. Buffett to stand and defend the system that allowed him to accumulate his vast fortune, or for other successful capitalists to speak up publicly for capitalism. It might have been a fine role for a well-educated and personable commodities trader, corporate lawyer, and Wal-Mart director, had she and her husband not decided instead to go into government work.