Edited sentence: A perverse incentive can arise when banning a good makes it more profitable to supply, by driving up the price.Advocates for a law banning a good or service often present the law as a way of getting rid of the banned thing.Banning does not make the banned goods or services go away -- all it does is threaten with prosecution those who are caught with the banned good or engaged in the banned service.For instance, prohibition (of alcohol) did not make alcohol use go away; rather, it drove it underground into the black market of speakeasies and moonshiners.However, the enactment of a ban rarely can cause the banned thing to suddenly disappear from society.Law enforcement is never perfect, so some people will be able to get away with breaking the law; this is why a black market is possible.Likewise, prostitution is illegal in most nations, but is still widely practiced.Similarly, the creation of a black market can create a profitable economic niche for organized crime