Mark Zuckerberg and Priscilla Chan’s decision to donate nearly all of their Facebook stock to philanthropic causes raises questions about influence, tax dodges, and democracy. Photograph by Andrew Harrer / Bloomberg via Getty

This post was revised to incorporate new information provided by Mark Zuckerberg in a Facebook post on December 3rd.

The announcement, on Tuesday, by Mark Zuckerberg and his wife, Priscilla Chan, that, during their lifetimes, they will donate to philanthropic causes roughly ninety-nine per cent of their Facebook stock, which is currently valued at close to forty-five billion dollars, has already prompted a lot of comment, much of it positive. That is understandable. The fact that Zuckerberg, Bill Gates, Warren Buffett, and a number of other billionaires are pledging their fortunes to charity rather than seeking to pass them down to their descendants is already having an impact.

Last year, the Bill & Melinda Gates Foundation, which was founded in 2000, dispensed almost four billion dollars in grants. A big slug of this money went toward fighting diseases like H.I.V., malaria, polio, and tuberculosis, which kill millions of people in poor countries. Zuckerberg and Chan have also already donated hundreds of millions of dollars to various causes, including eradicating the Ebola virus. In their latest announcement, which they presented as an open letter to their newborn daughter, on Zuckerberg’s Facebook page, they said that the Chan Zuckerberg Initiative, the new philanthropic organization that they are setting up, would focus on “advancing human potential and promoting equality.”

It’s not just the size of the donations that the wealthy are making that demands attention, though. Charitable giving on this scale makes modern capitalism, with all of its inequalities and injustices, seem somewhat more defensible. Having created hugely successful companies that have generated almost unimaginable wealth, Zuckerberg, Gates, and Buffett are sending a powerful message to Wall Street hedge-fund managers, Russian oligarchs, European industrialists, Arab oil sheiks, and anybody else who has accumulated a vast fortune: “From those to whom much is given, much is expected.”

Speaking at Harvard in 2007, Gates attributed this quotation to his dying mother. (A slightly different version of it appears in St. Luke’s gospel.) In 2010, Gates and Buffett challenged fellow members of the ultra-rich club to give away at least half of their wealth. Since then, more than a hundred billionaires have signed the “Giving Pledge.” Some of these mega-donors, such as Buffett, are content to let others direct their donations. (In 2006, he signed over much of his fortune to the Gates Foundation.) Increasingly, however, wealthy people are setting up their own philanthropic organizations and pursuing their own causes—a phenomenon that has been called "philanthrocapitalism.”

That is the positive side. It is also worth noting, however, that all of this charitable giving comes at a cost to the taxpayer and, arguably, to the broader democratic process. If Zuckerberg and Chan were to cash in their Facebook stock, rather than setting it aside for charity, they would have to pay capital-gains tax on the proceeds, money that could be used to fund government programs. If they willed their wealth to their descendants, then sizable estate taxes would become due on their deaths. By making charitable donations in the form of stock, they, and their heirs, could escape both of these levies.

The size and timing of the tax benefits to Zuckerberg and Chan are uncertain, but they are likely to be large. In the initial version of this post, based on the open letter Zuckerberg and Chan posted on his Facebook page, and on the opinions of several tax experts, I said that the couple, in donating stock to the new philanthropic organization, would gain immediate tax credits equal to the market value of the stock, some of which could be rolled over into future tax years. Typically, that is what happens when a rich person donates stock to a family foundation or to certain types of L.L.C.s constituted for philanthropic purposes, such as ones owned by family foundations.

On Wednesday, in a follow-up post on Facebook, Zuckerberg provided more details about the couple’s plans. Evidently, the L.L.C. that he and Chan are setting up will not be seeking tax-exempt status. “By using an LLC instead of a traditional foundation, we receive no tax benefit from transferring our shares to the Chan Zuckerberg Initiative, but we gain flexibility to execute our mission more effectively,” Zuckerberg wrote. “In fact, if we transferred our shares to a traditional foundation, then we would have received an immediate tax benefit, but by using an LLC we do not.”

Even if the Chan Zuckerberg Initiative doesn’t obtain tax-exempt status, over time its activities will most likely have a big impact on the taxes its founders pay. The I.R.S. treats ordinary L.L.C.s as “pass-through” structures, and shifting financial assets to such entities doesn’t usually generate any immediate credits or liabilities. But whenever the Chan Zuckerberg Initiative issues grants to nonprofit organizations, it will almost certainly do so by donating some of its Facebook stock, and that will generate tax credits for Zuckerberg and Chan equal to the market value of the stock at that time. As the years go by and the Initiative steps up its charitable activities, these credits seem likely to add up to very large sums.

Unlike a regular family foundation, the L.L.C. may also generate some tax liabilities for Zuckerberg and Chan. If it invested in a commercial enterprise, such as an online-learning company, taxes would be owed on any profits the investment generated. And if, as Zuckerberg also pointed out, the L.L.C. sold some of the Facebook shares that he and Chan have donated to it, they would have to pay capital-gains taxes on the proceeds. But since the couple will control the L.L.C., they will be able to decide how it finances itself, and whether it sells any stock.”

If what Zuckerberg is doing were an isolated example, it wouldn’t matter much for over-all tax revenues. But the practice is spreading at a time when the distribution of wealth is getting ever more lopsided, which means the actions of a small number of very rich people can have a bigger impact. In 2012, according to

By transferring almost all of their fortunes to philanthropic organizations, billionaires like Zuckerberg and Gates are placing some very large chunks of wealth permanently outside the reaches of the Internal Revenue Service. That means the country’s tax base shrinks. As yet, I haven’t seen any estimates of the over-all cost to the Treasury, but it’s an issue that can’t be avoided. And it raises the broader question, which the economists Thomas Piketty and Anthony Atkinson, among others, have raised, of whether we need a more comprehensive tax on wealth.

Arguably, there is another issue at stake, too: democracy.

Although organizations like the Gates Foundation portray themselves as apolitical, nonpartisan entities, they aren’t completely removed from politics. Far from it. The Gates Foundation, for example, has been a big financial supporter of charter schools, standardized testing, and the Common Core. (It has also given some money to public schools.) Zuckerberg, too, has also provided a lot of money to charter schools. They featured prominently in his costly and controversial effort to reform the public-school system in Newark, New Jersey, which Dale Russakoff wrote about in the magazine last year. In the letter posted on Facebook, Zuckerberg signalled that he isn’t done with such efforts. “We must participate in policy and advocacy to shape debates,” the letter said. “Many institutions are unwilling to do this, but progress must be supported by movements to be sustainable.”