Urban Density Versus Urban Farming

Many people, Matt Yglesias  for one, believe in urban density, arguing that it's efficient, supports interesting lifestyles, helps the environment, etc. etc.  Many of the same sort of people (i.e., highly educated types) believe in the food movement, some of whom believe in urban farming.   There's tension between the two principles.  This piece in Modern Farmer on the battle over converting an urban garden to an urban hospital shows the tension.