How valuable are public parks? This light-hearted debate features two endearingly nerdy policy wonks going shot-for-shot.

Waste of Space  Matthew Yglesias doesn't care for parks. "I'd rather see this land put to use with buildings and stuff," he wrote of plans to expand parks in Washington, D.C. "It's not clear to me that we're suffering from a park shortage. And in environmental terms, it's much better for the planet to construct additional housing units in already-urbanized areas than to pack a bit more green space in the city and have more people living in sprawling exurbs."

Think of the Children  The New Republic's Jazon Zengerle quipped, "I have a hunch his thinking might change if/when he has a kid." Added Andrew Sullivan, "Or a beagle."

Consider Housing Costs  Yglesias, however refused to be waved off. "I never find this to be a particularly useful way of talking about a policy issue," he responded, saying that his opinion on "the home mortgage interest tax deduction" didn't change when he mortgaged his home. Yglesias argued that if cities want to help kids, they should develop parks into cheap housing, thus increasing the supply of homes and reducing the cost. "Cheaper housing is strongly pro-family, since people with kids obviously need more square feet per income-earner," he wrote, concluding, "A little patch of empty green space looks nice, but it's a bad way to use a scarce resource."

Akin to Free Housing Addition  Zengerle rebutted that, if Yglesias had the "life experience" of raising kids, he would support expanding parks on the same grounds he now opposes it. "Kids need a lot of space--much more than many people could ever possibly afford to own or rent themselves in a city," he wrote. "That's where parks come in. In some ways, they serve as an addition to your home--and a public one at that." Zengerle argued that parks also promote health. "That's not even getting into the whole issue of fresh air, exercise, etc., that are obviously beneficial to children," he added.