Chrystia Freeland, global editor-at-large at Thomson Reuters, is the author of "Plutocrats: The Rise of the New Global Super-Rich and the Fall of Everyone Else.''

Charity is a virtue -- and it is one of the great, traditional strengths of U.S. civil society. The problem is that as the gap between the rich and everyone else increases, among the super-elite there is a creeping temptation to conflate charity with taxation.

This idea is captured in a term Foster Friess, the wealthy Wyoming philanthropist and conservative political activist, coined in an interview with me: the self-tax.

Collectively, democratically, we raise money and spend it. How else would we pay for unglamorous services that charities overlook?

"People don't realize how wealthy people self-tax," Friess replied, when I asked whether taxes on the rich should rise. "You know, there's a fellow who was the C.E.O. of Target. In Phoenix, he's created a museum of music. He put in around $200 million of his own money. I have another friend who gave $400 million to a health facility in Nebraska or South Dakota, or someplace like that. You look at Bill Gates, just gave $750 million, I think, to fight AIDS."

"I think we should get rid of taxes as much as we can," Friess explained. "Because you get to decide how you spend your money, rather than the government. I mean, if you have a certain cause, an art museum, or a symphony, and you want to support it, it would be nice if you had the choice to support it. Where we're headed, you'll be taxed, your money taken away, and the government will support it."

"It's a question -- do you believe that the government should be taking your money and spending it for you, or do you want to spend it for you?"

From the point of view of the person writing the check, the appeal of the self-tax is self-evident: you get to choose where your money goes and you get the kudos for contributing it.

But for society as a whole, the self-tax is dangerous. For one thing, someone needs to pay for a lot of unglamourous but essential services, like roads and bank regulation, which are rarely paid for by private charity.

Even more crucially, the self-tax is at odds with a fundamental democratic principle -- the idea that we raise money collectively and then, as a society, collectively choose how we will spend it.

Philanthro-capitalism, as its fans have dubbed the muscular and innovative charitable giving favored by today's super-rich, can be an energetic contribution to global civil society. But it must not replace or, worse yet, usurp, public policy as formulated and implemented by our society as a whole. That is called democracy, and it takes taxes, including those paid by the philanthro-capitalists, to pay for it.