Throughout history, rulers have proposed, and reality has disposed. From Charles Hugh Smith at oftwominds.com:
In effect, authorities created two rat farms, both unintended: the sewers, and the private-sector rat-farms.
The history of Rat Farms offers a valuable lesson in how markets and bureaucracies work.
The story of how the colonial authorities in Hanoi came to establish two kinds of rat farms is highly instructive.
The first rat farm was unintentional. French colonial authorities decided to modernize the French Quarter of Hanoi (where Westerners lived) by constructing a modern sewer system, the overall goal being to establish “a little Paris in the East.”
Their understanding of sewers was limited to the first-order effects: sewers safely collected and disposed of human waste.
They did not anticipate the second-order effect: the sewer was Rat Paradise, as “the pipes offered rats a new ecological niche, free of predators and full of food.”
Second-order effects generate unintended consequences. (First-order effects: actions have consequences. Second-order effects: consequences have their own consequences.)
Rats proliferated in the sewers and began roaming the streets of Hanoi–not exactly the results intended by the authorities.
Matters became worse when in 1902 a first case of bubonic plague was detected. Modernity had created a potential health crisis.