Unintended consequences are quite common and sometimes counter-intuitive:
Paul Krugman offers a sad example of good intentions gone awry: "In 1993, child workers in Bangladesh were found to be producing clothing for Wal-Mart and Senator Tom Harkin proposed legislation banning imports from countries employing underage workers. The direct result was that Bangladeshi textile factories stopped employing children. But did the children go back to school? Did they return to happy homes? Not according to Oxfam, which found that the displaced child workers ended up in even worse jobs, or on the streets—and that a significant number were forced into prostitution". Oops.
Source: Charles Wheelan. Naked Economics: Undressing the Dismal Science. WW Norton & Company, 2010. [B047]
Exposure to the sun may not be as bad as advertised:
Reduce your exposure to the sun, the logic goes, and skin cancer rates fall. True enough. Guess what goes up when sun exposure goes down, though: blood pressure. And as blood pressure climbs, so do rates of heart disease and stroke. People who avoid the sun have higher overall mortality rates than do people who seek it.
Source: Heather Heying and Bret Weinstein. A Hunter-gatherer's Guide to the 21st Century: Evolution and the Challenges of Modern Life. (2021). [B148]
Here's another example of good intentions gone awry:
Consider another example in which. Mexico City is one of the most polluted cities in the world; the foul air trapped over the city by the surrounding mountains and volcanoes has been described by the New York Times as "a grayish-yellow pudding of pollutants". Beginning in 1989, the government launched a program to fight this pollution, much of which is caused by auto and truck emissions. A new law required that all cars stay off the streets one day a week on a rotating basis (e.g., cars with certain license plate numbers could not be driven on Tuesday). The logic of the plan was straightforward: Fewer cars on the road would lead to less air pollution. So what really happened? As would be expected, many people did not like the inconvenience of having their driving days limited. They reacted in a way that analysts might have predicted but did not. Families who could afford a second car bought one, or simply kept their old car when buying a new one, so that they would always have one car that could be driven on any given day. This proved to be worse for emissions than no policy at all, since the proportion of old cars on the road went up, and old cars are dirtier than new cars. The net effect of the policy change was to put more polluting cars on the road, not fewer. Subsequent studies found that overall gas consumption had increased and air quality did not improve at all. [Again] good intentions led to a bad outcome because the incentives were not fully anticipated.
Source: Charles Wheelan. Naked Economics: Undressing the Dismal Science. WW Norton & Company, 2010. [B047]