My grandmother, who is 90 but acts about half that, is fond of preaching moderation in all things. She has a point. 

One slice of pizza is satisfying. Seven is a stomachache. Working is preferable to unemployment, but 16-hour days make you question the advantages. A little bit of a virus is called a vaccine; a bit more is called the flu. 

In large doses, just about anything can be bad for you. Even vitamins—essential for health—are deadly in excess.

The same is true of residential diversity. Neighborhoods with a sprinkling of low-income families function fine. But one need not walk through the Marcy Houses at midnight to appreciate the dangers of concentrated poverty.

By itself, being poor is bad enough. But cramp lots of underprivileged and overlooked people into a cauldron of stress and deprivation and you have the perfect recipe for just the sorts of social ills society spends billions trying to avoid.

Despite longstanding recognition of the degenerative—yet remarkably reproductive—effects of concentrated poverty, America remains starkly separated by class.

Even in a globalized e-universe, it’s hard to overstate the importance of place in determining life chances. High poverty neighborhoods are crowded, noisy, and stressful. They lack good schools and good jobs. Welfare offices take the place of banks and businesses. Their chief export is crime.

The consequences are predictable. Preoccupation with daily needs compromises cognitive functioning. Overexposure to human suffering coupled with underexposure to supportive resources is physically destructive and psychologically damaging.

Inexperience with anything else attenuates ambition and curtails expectations. What you see is what you get. Geography becomes fate.

Children who grow up there are less likely to succeed, or even survive. If stray bullets or drugs don’t get them, lack of recreational spaces and healthy food options will.

Sadly, there’s more to it: as all-too-often is the case, “class” is a euphemism for “race.” Segregation may be a thing of the past at lunch counters and on public buses, but when it comes to housing patterns, America remains depressingly, distressingly divided along racial lines.

In political discussions today we like to debate red states vs. blue states and going green vs. earning green. But the real polarization of America’s color palette is steadfastly black and white.

According to research at Brown University, the typical white household lives in a neighborhood that is three-quarters white, while the average black neighborhood is 41 percent black – despite the fact that blacks represent just 12 percent of all households.  

The ethno-economic divide is staggering. The average black family lives in a neighborhood where a fifth of people are poor, double that of the average white family. Most striking, affluent black households live in areas that are poorer than the places where poor white households live. And as the Urban Institute points out in its update to the Moynihan Report, nearly all high-poverty neighborhoods (poverty rate greater than 40 percent) are majority-minority.

Part of it is sorting. People prefer to live near others they perceive to be like themselves.

Part of it is the continued legacy of America’s troubled racial past. According to a Department of Housing and Urban Development report released last week, one in ten blacks faces discrimination in the housing market—and that’s the low estimate.

And part of it is a failure of public policy.

As TCF fellow Stephanie DeLuca has documented, the scourge of concentrated poverty has been appreciated for decades, yet policy has been slow to respond. Even as public housing projects were torn down at an accelerating rate in the 1990s and federal policy came to emphasize tenant-based housing subsidies, residential mobility has scarcely improved.

Currently, national affordable housing policy is dominated by two programs. On the demand-side, the $16 billion Housing Choice Voucher program (HCV, also known as Section 8) covers 70 percent of rent for 2.1 million low-income families. On the supply-side, the Low Income Housing Tax Credit program (LIHTC) has created 2.2 million affordable units in its 25 years of existence, by providing about $8 billion annually in development subsidies.

Both make housing more affordable. But both are flawed.

The voucher program is plagued by shortages and years-long waiting lists. As DeLuca discusses, this –along with time limits for apartment searches, a scarcity of suitable units, and a lack of institutional incentives for the decentralized public housing authorities that operate the program—has resulted in little poverty deconcentration. Fewer than one in five black voucher holders live in neighborhoods where the poverty rate is less than 10 percent.

For its part, the LIHTC program, which can serve households up to 60 percent of median income, often excludes the neediest families – and when it does serve them, may only exacerbate existing poverty concentration by building in already-poor neighborhoods.

This sorry state of affairs doesn’t need to last. The fixes are relatively straightforward, even if the political will is not.

Simply put, housing is not an American priority. Our safety net provides guarantees for food and health, but we lack a national right to humankind’s third basic necessity: shelter.

Just one in four Americans who qualify for housing vouchers receive them – and many who do are consigned to substandard dwellings replete with vermin and environmental hazards. Three in five black households spend more than 30 percent of their income on rent, the level generally considered affordable.

One way to finance “shelter stamps” would be to reduce our systematic bias for homeownership. The government spends in excess of $70 billion annually on the mortgage interest deduction—and that’s not even including the invisible value of imputed rent (that is, homeowners are not taxed on the “rental” income they effectively pay to themselves for residing in the houses that they own).

The vast majority of these benefits flow to affluent households. As it stands, such preferential treatment is de facto discrimination: just 43 percent of blacks own houses, compared with 70 percent of whites.

Expanding the emphasis on mobility as a performance measure for the voucher program would also help. So too would regionalizing program administration, which would reduce unnecessary parochialism in placements and encourage cross-jurisdictional moves.  At the same time, LIHTC regulations could be tightened to favor needier families.

As Heather Schwartz’ research for TCF has found, smart housing policy has valuable spillover effects. Housing policy is school policy: residential integration promotes education integration—and leads to markedly improved academic outcomes among low-income students.

When it comes to combating poverty and inequality, spreading the wealth would help. But so would spreading the poor.