One of the signature features of the modern age is the bottomless greed of the global economic elite. The richest people in the world — business tycoons, political elites, and wealthy heirs — spend half their time attempting to rake in more cash, and the other half protecting what they already have from as much taxation as possible. The key tool in this latter process is the tax haven: using legal chicanery (and, rather frequently, straight-up fraud) to move income and wealth into jurisdictions where it will be subject to little or no tax.

Tax havens have been an obvious problem for decades. But they've gotten special attention from the publication of leaked corporate documents in the Panama Papers, and most recently, the Paradise Papers.

Tax avoiders use all sorts of techniques. But I'd like to focus on one: real estate. It's a technique that is both growing in importance, and could be addressed relatively easily.

First, it's important to be clear about what sort of behavior tax avoidance is. All corporations and businesses rely absolutely on states to exist at all. No entrepreneur could ever get going without a state-created legal system, state-enforced property rights, and the state monopoly on violence. Using a tax shelter is therefore sheerest economic parasitism — rolling up a big pile of wealth under the umbrella of state protection, and then squirming out of as much responsibility as possible to maintain that state.

Real estate — especially in red-hot, ultra-expensive markets like Manhattan — has become a favored investment vehicle for the global elite. As this New York investigation demonstrates, between 2008 and 2014, roughly 30 percent of condos in big Manhattan developments were sold either to foreign investors or LLCs (which are usually hiding some foreign investor).

Foreign investors do generally have to pay some American tax (in property and sales), for the privilege of avoiding domestic taxation in Russia or wherever. But they are clearly getting a good deal out of it — there are only so many places to sock away millions, especially in ways which camouflage one's identity.

Indeed, U.S. real estate especially has certain advantages over small tax havens. Places like Bermuda or Seychelles are tiny and would be defenseless if they ever came under U.N. sanctions or even serious pressure from a major world power. New York real estate, in addition to being a handy wealth storage mechanism that provides a place to land anytime one feels like visiting New York City, is free from such threats — and reaps the gains of any increases in the market, which have been spectacular in New York of late.

The flood of outside cash rolling into New York real estate has numerous downsides. Most obviously, it drives up prices for actual New Yorkers who are looking to buy. But it also drives up rents, by keeping many perfectly good apartments empty. Many foreign investor properties are rented out, but many are not. Per the New York article: "The Census Bureau estimates that 30 percent of all apartments in the quadrant from 49th to 70th Streets between Fifth and Park are vacant at least 10 months a year."

Second, a great many of the foreign investors and associated shell companies are laundering money. The alleged money laundering scheme of Paul Manafort — President Trump's former campaign chairman who was recently indicted — involved New York real estate. The New York Times spent enormous effort looking into just a handful of high-end Manhattan residential buildings, and found a slew of extremely shady and occasionally illegal foreign investors. Activists leaked a report describing elite American attorneys — including a "recent president of the American Bar Association" — giving advice about how to move shady cash into the country, and one of the prime methods was buying New York real estate.

More broadly, back in March 2016, the Treasury Department decided it would start tracking the purchase of real estate by secret foreign buyers, just in Manhattan and Miami-Dade County. A few months later, they found that over a quarter of all the cash purchases of luxury apartments were suspicious, and expanded the effort. Nothing is completely proven, but it's a safe bet this stuff is rampant.

Something similar holds for London — as economist Gabriel Zucman, an expert on hidden wealth, writes, "Why do we allow a great chunk of Manhattan and London to be owned by faceless shells, potentially hiding criminals and money launderers?"

So what might be done? First, there needs to be an all-out assault on money laundering. Enforcement of these laws has been so lax of late that criminals have become extremely sloppy, so many properties might be easily seized. Second, municipalities like New York could ban foreign shell companies from purchasing residential property, and perhaps institute a residency requirement, saying an apartment must be occupied at least eight months a year or be repossessed.

There are probably other methods as well. But the important thing to keep in mind is that foreigners using U.S. real estate as a safe deposit box are parasites. New York City is a valuable place to buy real estate because it is the cultural and financial capital of the world's most powerful nation — and because millions of Americans live there. By all means, New York City should welcome genuine immigrants as it always has. But outside of the self-interest of a handful of rich real estate agents and property developers (who absolutely would not go begging if foreign investment was sharply curtailed), there is no reason to allow ultra-rich tax avoiders to use American institutions — badly distorting the housing market for actual New Yorkers in the process — for their own greed and nothing else.