Interesting hypothesis. Mine would be the opposite, that great cities are a result of an advancing culture. An agrarian/rural society cannot long last without a commerce center, and one would naturally spring up and undergo a typical urban cycle of boom, economic decay, moral decay, and finally - voting for democrats. The best way to deal with the blue-zoners is probably to kick out or lock up the lunatics. The empty hull of the city would provide excellent opportunity and eventually fill with red-zoners.
There are several illuminating books about the origins and functions of cities. Jane Jacobs wrote several and Lewis Mumford a classic. They show the vital necessity of cities in producing civilization as the origin of the word itself also shows. Initially it provided a market, a citadel and a place for the temple.
Advancement past the agricultural stage does not occur without the city. Development stagnates without strong urban life and history confirms this. Ideas good and bad flow from the cities to the hinterlands surrounding them. A more accurate view of the relation between urban and rural areas is that the former sweeps up the latter in its cultural/economic orbit and without their urban dynamism rural progress falls away and stagnation and poverty results.
Much, if not most, of the negative aspects of cities comes from the lower classes which go there seeking a chance of improvement and opportunity those that fail often turn to lives of crime and/or welfarism. Those who actually make the city work: taxpayers, police, firemen etc. are more conservative than the city as a whole. Democrats have always sought the failures, ne'er-do-wells and parasites to form the base of the party. Thus the first welfare was that provided by the RAT party bosses in exchange for votes. It has become institutionalized and part of the governmental structure.