Our distant ancestors built Rome and Jerusalem and Xi'an and Teotihuacan. Our more recent ones Kyoto and Buenos Aires and Paris and Marrakesh, and many more of humanity's timeless cities. And most of them did it not through vast infusions of wealth, but through many average citizens working incrementally. You don't have to be wealthy by modern standards to create a great place and maintain it. The genius of the traditional development pattern is exactly that: your place has the potential to thrive in the future even if the people living there then are of modest individual means.

3. Your suburban town probably can't afford its development pattern even if it is rich.

Here's a common sense observation: There is a limit to the amount of public obligation we can take on. And that limit is separate from any question of short-term cash flow or debt financing—i.e. the ability to write the checks today and have them clear.

Reductio ad absurdum: Suppose we built Elon Musk's Hyperloop and connected every city over a million people in the U.S. to the system. Could we afford to do it? If someone were willing to lend us trillions of dollars, sure, in a sense we'd be able to "afford" it: we'd have a loan through which we could pay contractors to make construction happen. Would it be a good idea? No. It'd be completely insane.

So we should all be able to agree there is a theoretical limit on the amount of infrastructure we can afford per capita. This is obvious and trivial. What we're arguing about is where the line is between affordable and not affordable, sustainable and not sustainable. Crucial to the Strong Towns argument is that the line isn't where you think it is.

We've been living so long with an illusion of wealth that we assume, "We must be able to afford all this stuff we've built, because it exists."

Reductio ad not-so-absurdum: If the state of Georgia wanted to double its road network, and someone were willing to lend the Georgia DOT the money to do it—backed by promises that the new capacity would unleash a virtuous cycle of economic growth and the investment would pay for itself—it could do so. If the debt financing were available, humans could be put to work building those roads, and then they'd exist.

I bet most readers will agree that this would be over-the-top. That wave of economic growth wouldn't materialize, because road spending doesn't really create much prosperity; it just tends to move it around by enabling people to live and work in new places and commute longer distances. Georgia would be stuck with a lot of expensive pavement in need of eventual maintenance.

Georgia currently has an estimated 271,000 lane miles of public road. The cost of a new road is highly variable but let's go with a lowball estimate of $1 million per lane mile. The state could double its existing road network for the low, low price of $271 billion. Divided over 30 years (a reasonable estimate of the lifespan of a road) and 10.43 million current Georgia residents, that's $866 every year for 30 years for every man, woman, and child in the state of Georgia. (Note for the nerds in the crowd: Yes, this is extremely simplistic in countless ways—it's a thought experiment, not a fiscal analysis.)

That's just roads: what if we also doubled the extent of sewers, water mains, pump stations, treatment plants, sidewalks, and so forth? And keep in mind the state has still got to maintain all of the stuff it's already built.

The thing is, this isn't actually that preposterous. Because we have done it before, and in a place without Georgia's booming growth. As Jason Segedy points out, Cuyahoga County, Ohio—home to Cleveland—more than doubled its built footprint from 1948 to 2002, while its population ended up being exactly the same in both years: 1.39 million.

Cleveland built a whole new Cleveland for no net new residents. And we wonder why we're going broke.

Suburban Atlanta can be smug and say, "But Cleveland is a Rust Belt city. It's been in decline for decades. We're growing."

Oh yeah? For how long are you going to keep that up? What happens when you don't grow?

So let's lay to rest the excuses of those who claim that the math about the unsustainable cost of infrastructure under the suburban development pattern doesn't apply to them:

"No one would lend us this money if it weren't a good investment."

"We wouldn't take on this debt if it weren't a good investment."

"Our growth itself is proof that we're doing something right."

"Well-to-do people keep moving here, so we must be doing something right."

"A government budget isn't like a household budget. We take on debt today in order to spur the economic activity that will pay down the debt tomorrow."

Sure, some municipal investments do pay off multiple times over—but the onus is on the government to do a rigorous cost-benefit analysis, absent the hand-waving that typically accompanies assertions that new spending is an investment in growth.

This isn't a small-government argument. It's actually agnostic to the normative question of how small or large local government ought to be. If you, the residents of an affluent community, want to tax yourselves more to invest in your quality of life, go for it. But can you back out of that obligation if your circumstances change?

Infrastructure is perilous because it's physically permanent. Cannibalizing your future tax base, via TIF or another means of jump-starting development right now, is perilous. When you commit your children's generation to paying for something you built, you need to think differently about that decision: because you don't know their situation, or even who will be living in your city then.