I've been having this discussion concurrently with my cousin, who lives among the cornfields of Minnesota, and with a couple fellow gardeners at our local community garden. And here's what I'm thinking.
Proponents of sustainability, and improving the quality of life in urban environments, and improving the American diet, have supported urban farming for decades and decades. Carving out sustainable and productive spaces where we live and work seems like a no-brainer. But opponents of urban farming (and often organic farming, and the local food movement) say that urban farming will never be economically self-sustaining or produce enough food to meet the demand. And these claims are probably true, but are they relevant? And are they as decisive as they're taken to be by the people who utter them?
Most urban farm projects do require grants and foundational funds to keep them afloat. And since the space available is limited, the amount of food they can produce is also limited. These things are true. But this only tells half the story. These same people who bash organic and urban farms are big supporters of rural conventional farming. And rural conventional farms are not economically self-sustaining either. They get loads of money every year. Their money comes from the government rather than from private donations, but what of it? The point is, if capitalist standards are the only standards that apply, then no farming is worthwhile.
Obviously farming is necessary, since everyone, from the most ruthless capitalist to the most idealistic flower child, must eat. But if you step outside the capitalist values that dominate in our culture, there are all kinds of other reasons why urban farming is worthwhile. Urban farms reduce the oil used in transporting food to the city. They provide clean soil and open spaces that can serve as a respite from the stresses of life in the city. They provide educational opportunities and jobs for at-risk youth who have few options open to them. Meanwhile, government-sponsored conventional farms produce toxic runoff, deplete the soil, rely heavily on oil-based chemicals, and utilize an exploitive labor system. And they're still not profitable.
So it seems to me that the calculus that we use to determine which types of agricultural practices pay off are extremely skewed. Selectively choosing which costs and benefits to factor in is a great way to get the result you want out of any analysis, but all that's revealed are your personal biases and political/economic interests.
Beyond this issue, the kind of reasoning involved here assumes that one must adopt an all-or-nothing stance. For instance, some will argue that organic farming is a waste of time because you could never produce enough bushels per acre to feed the world with organic farming alone. First, this claim is extremely controversial and basically unsubstantiated, but second, this doesn't count as a reason not to support organic farming. A similar claim is that urban farming alone can't feed a city, and neither can the efforts of individual families in their own backyard gardens and chicken coops. So this is a reason not to support them?
Every bushel of produce that comes out of a sustainable urban space is one less bushel that needs to be produced with the toxic industrial methods that are so terrifically unsustainable. And every family that has increased access to clean and healthy foods is one less family that's likely to be caught in an unhealthy inter-generational cycle. And every productive urban space makes a small dent in our oil consumption, as well as in the accompanying air pollution and toxic runoff that oil consumption leads to. These are reasons enough to support urban farming, even within a capitalist value system that is incapable of recognizing the value of nonmarketable goods.