Aaron Renn has an interesting article in Governing. He suggests that even though urban cores are responsible for a significant chunk of the regional tax base, “[t]he city is dependent on the suburbs, too.” In particular, he notes that downtowns are dependent on a labor and consumer pool that extends far beyond downtown. For example, Manhattan is valuable because it is at the center of a vast region.
He’s right- if you define “suburb” broadly as “everything that isn’t downtown.” A downtown that isn’t surrounded by neighborhoods is just a small downtown.
But that isn’t always the way Americans understand suburbs. If you think of suburbs as “towns outside the city with a different tax base that are usually much richer than the city” , suburbs aren’t good for the city at all. Because of the growth of suburbs, cities have stunted tax bases because they have a disproportionate share of the region’s poverty, and have to pay for a disproportionate share of poverty-related government programs. By contrast, if cities resembled the cities of 100 years ago that included nearly all of their regional population, they would have stronger tax bases. (This may seem like a pipe dream to residents of northeastern cities trapped within their 1950 borders, but plenty of Sun Belt cities include huge amounts of suburb-like territory).
Similarly, if you think of suburbs as “places where most people have to drive to get anywhere” their existence is not so good for the city. When suburbanites drive into the city they create pollution, and they lobby for highways that make it easier for them to create even more (while taking up land that city residents would otherwise use for businesses and housing). And when jobs move to car-dependent suburbs, that devalues city living, either because carless city residents are frozen out of those jobs, or because city residents have to buy cars to reach those jobs (which sort of defeats the point of city living, insofar as short commutes are an advantage of city life).
To put it another way, a city needs neighborhoods outside a central business district. But it benefits far less than it otherwise would if those neighborhoods are car-dominated or outside city limits.