Urban farming would be a great idea if it encouraged the principle of homesteading, whereby individuals acquire title to real property that is either unowned, or has been abandoned. Many vacant lots in inner cities could properly be considered abandoned. Urban farming is a bad idea because it seeks co-operation with State and local governments. But Governments are the prime reason that land has been abandoned in the inner cities, and they are the force which keeps it as such, so that individuals in their own capacity cannot acquire that land through homesteading.
Instead, States actively engage in evicting people from land that nobody owns, and I’ve heard stories of “urban farms” being effectively repossessed by governments under eminent domain laws, in the past.
Urban farming would be a great idea if it argued from a natural rights perspective, that man may acquire unowned or abandoned property by transforming it from a state of nature. Instead, they argue from a social-utilitarian perspective; that people need this, therefor government should provide it or permit it.