Edward L. Glaeser is an economics professor at Harvard.

Jane Jacobs is one of history’s greatest urban thinkers. In most areas, Jacobs was a peerless analyst of urban life. She understood the virtues of busy neighborhoods, the economic opportunity that comes from urban innovation and the value of small firms and industrial diversity. She even presciently grasped the fact that cities are good for the environment, a point that I have re-emphasized in a past post.

But she wasn’t always right.

Her view of city life, expounded most eloquently in her 1961 classic “The Death and Life of Great American Cities,” drew heavily on her own experience living in Greenwich Village. She saw so clearly the very real virtues of moderate densities and older buildings, like those found in the Village, that she became too friendly toward historic preservation and too hostile towards high density levels. I’ll address historic preservation next week and focus here on Jacobs’s unfortunate fear of heights.

Here are some of her own words:

“It follows, however, that densities can get too high if they reach a point at which, for any reason, they begin to repress diversity instead of to stimulate it. Precisely this can happen, and it is the main point in considering how high is too high.”

“For most districts …. The ultimate danger mark imposing standardization must be considerably lower; I should guess, roughly, that it is apt to have at about 200 dwellings to the net acre.”

Her preferred density level seems to have been about 150 housing units per net acre, which means six-story buildings if units average 1,600 square feet. Six stories also seems to be the maximum height that people are willing to walk up regularly, which may explain why it is the norm in many older pre-elevator areas.

Now I don’t have anything against Greenwich Village or six-story buildings, but the perspective of the economist pushes strongly against any attempt to postulate or, far worse, regulate a single perfect density.

Indeed, to anyone who respects consumer sovereignty, there is something a little jarring about Jacobs’s question: “What is the proper density for city dwellings?”

Why in the world should there be a “proper density”? A good case can be made that cities succeed by offering a diverse menu of neighborhoods that cater to a wide range of tastes. Some people love Greenwich Village, and that’s great, but I was perfectly happy growing up in a 25-story tower, and I don’t see anything wrong with that, either.

Jacobs was reacting to the Le Corbusier-inspired public housing passions of the 1950s, when tall structures reflected the passions of planners more than consumer demand. Jacobs was right to emphasize that shorter neighborhoods also have tremendous virtues. I’ve actually tested Jacobs’s hypothesis that city streets are safer when buildings are shorter and found some evidence, admittedly debatable, supporting her view. But Manhattan’s crime levels have fallen dramatically in recent decades, proving that with sufficient policing, safe streets can be perfectly compatible with tall buildings.

Jacobs feared high densities because she thought that they would lead to too little diversity, but there are good reasons to think that she get things backward. Restricting new construction and keeping buildings artificially low means that housing supply cannot satisfy demand. The result is high prices and cities that are increasingly affordable only to the prosperous.

The laws of supply and demand are not subject to legislative appeal. When demand for a place is strong, as it has been in New York since the 1970s, then that place must either build substantially or experience rapidly rising prices. Yet despite skyrocketing prices, building dramatically slowed in Manhattan between the 1960s and the 1990s. Even more remarkably, the height of new residential buildings seems to have substantially declined.

This decline in heights doesn’t reflect a lack of demand for tall buildings; the high prices paid for units in Manhattan’s aeries belie that interpretation.

Market forces pushed for taller structures, but structures got shorter, at least until the Bloomberg years, because of a regulatory environment that made construction increasingly more difficult. My work with Joseph Gyourko and Raven Saks suggests that perhaps one-half of the cost of a Manhattan condominium can be understood as the price of land-use regulation.

Restricting supply led to higher prices and a city with space only for the rich. In the 1950s and 1960s, middle-income people, like Jane Jacobs and my parents, could afford Manhattan. Equivalent families today can’t afford the city, and that’s a pity. By contrast, Chicago, with its longstanding pro-construction ethos, remains far more affordable even in prime locations.

If you love cities, then you should want more people to be able to enjoy them, and that means embracing, not eschewing, densities over 200 units per acre. Certainly I experienced plenty of diversity and street life in the tall, rental building where I grew up.