Chairman Mao thought killing all the sparrows in China (part of his Four Pests Campaign[1]) would be a great idea because they ate laborers' grain seed. But the

Chairman Mao thought killing all the sparrows in China (part of his Four Pests Campaign[1]) would be a great idea because they ate laborers' grain seed. But then the population of crop-eating insects ballooned, causing the Great Chinese Famine to get a lot worse. Tens of millions starved to death. [1]: https://en.wikipedia.org/wiki/Four_Pests_Campaign https://en.wikipedia.org/wiki/Four_Pests_Campaign