One of my favorite anecdotes that exemplifies unintended consequences is one call “Bootleggers and Baptists”. Wikipedia has a decent explanation.

If you want to skip the link and get the summary it goes something like this:

It isn’t often that you find bootleggers and baptists on the same side of the fence. Consider moral laws that prevent merchants from selling booze on Sunday. Now a baptist would wish alcohol not be sold at all, and especially on the day God rests. Afterall, would you really want drunks out on the road while all of the fine church-going folk are spending time with their families?

The problem that most people miss is that the bootleggers are more than happy to sell alcohol when the churchgoers are busy praying and singing. They could charge a markup specifically because the law does not permit alcohol sales on Sundays.

If you’re not too slow, you might see the bit of the paradox arising. If someone were to challenge the law because it is absurd on its face, you end up with the bootleggers and the baptists on the same side of the voting booth. Bootleggers would end up with very little money and the baptists would lose out on forcing their moral superiority on anyone who doesn’t agree.

A bootlegger therefore has to do very little if the baptists pursue keeping alcohol sales illegal on Sunday. In fact, they will throw as much support behind the baptists as possible if they were smart.

Whodathunkit.