John Kenneth Galbraith wrote that all financial crises are the result of “debt that, in one fashion or another, has become dangerously out of scale.” The recent financial crisis was no exception, with everyone—homeowners, private-equity investors, our biggest banks—taking on enormous amounts of debt. If it’s frustrating that the government is footing the bill to clean up the mess, it’s even worse that the government helped pay for the debt binge that created the mess in the first place, thanks to a tax system that actually subsidizes borrowing. Debt didn’t get dangerously out of scale because the system was broken. It got out of scale, in part, because the system worked.

Illustration by Christoph Niemann

The government doesn’t make people go into debt, of course. It just nudges them in that direction. Individuals are able to write off all their mortgage interest, up to a million dollars, and companies can write off all the interest on their debt, but not things like dividend payments. This gives the system what economists call a “debt bias.” It encourages people to make smaller down payments and to borrow more money than they otherwise would, and to tie up more of their wealth in housing than in other investments. Likewise, the system skews the decisions that companies make about how to fund themselves. Companies can raise money by reinvesting profits, raising equity (selling shares), or borrowing. But only when they borrow do they get the benefit of a “tax shield.” Jason Furman, of the National Economic Council, has estimated that tax breaks make corporate debt as much as forty-two per cent cheaper than corporate equity. So it’s not surprising that many companies prefer to pile on the leverage.

There are a couple of peculiar things about these tax breaks—which have been around as long as the federal income tax. The first is that they’re unnecessary. Few people, after all, can save enough to buy a home with cash, so home buyers naturally gravitate toward mortgages. And businesses like debt because it offers them tremendous leverage, making it possible to put down a little money and potentially reap a huge gain. Even in the absence of the deductions, then, there would be plenty of borrowing. The second thing about these breaks is that their social benefits are pretty much nonexistent. Advocates of the mortgage-interest deduction, for instance, claim that it increases homeownership rates. But it doesn’t: in countries where mortgage deductions have been eliminated, homeownership rates haven’t dropped. Instead, the deduction simply inflates house prices. The business-interest deduction, meanwhile, may lower an individual company’s taxes, but it also means that the over-all corporate tax rate is higher, so its real impact is to give companies with lots of debt an unjustified advantage.

If the benefits are illusory, the costs are all too real. Economies work best, generally speaking, when people are making decisions based on economic fundamentals, not on tax considerations. So, as much as possible, the tax system should be neutral between debt and equity, and between housing and other investments. It’s not, and, worse still, as we’ve seen in the past couple of years, debt magnifies risk: if companies or individuals rely on large amounts of leverage, it’s much easier for bad decisions to lead to insolvency, with significant ripple effects in the wider economy. A debt-ridden economy is inherently more fragile and more volatile. This doesn’t mean that the tax system caused the financial crisis; after all, the tax breaks have been around for a long time, and the crisis is new. But, as a recent I.M.F. study found, tax distortions likely made the total amount of debt that people and companies took on much bigger. And that made the bursting of the housing bubble especially damaging. So encouraging people to take on debt qualifies as a genuinely bad idea.

But it’s not an easy situation to change. In 2005, a special Presidential panel on tax reform actually proposed eliminating the business-interest deduction and severely restricting mortgage-interest tax breaks. Those proposals, predictably, went nowhere. But we’re in a different historical moment now: the perils of too much borrowing have never been clearer. And there are precedents, on a smaller scale, for these kinds of changes. In the U.S., people used to be able to write off the interest they paid on credit cards. That tax break was abolished in 1986, and, the same year, the mortgage-interest deduction, which used to be unlimited, was capped. Great Britain, meanwhile, abolished its mortgage tax break in 2000. Similarly, there are a number of countries, including Brazil and Belgium, that don’t give corporate debt a tax advantage over equity, while, just last year, both Germany and Denmark cut back sharply on their business-interest tax breaks, limiting how much interest companies can write off. Given the weak state of the economy and of housing prices, a wholesale rewriting of the tax code may be a bridge too far right now, but there are plenty of reforms—capping deductions, phasing them out over time, restricting their use by heavily leveraged companies—that would move in the right direction.

The clearest hurdle to these changes may be political, but the bigger hurdle is, in a way, psychological: because tax breaks on debt have been around so long, we can hardly imagine what it would be like if we changed them, and we tend to underestimate their influence in shaping our behavior. Subsidizing debt seems harmless simply because we’ve always done it. But the fact that you’ve had a bad habit for a long time doesn’t make it less dangerous. ♦