The basic principle in Western democracies is the rule of law. That means, at minimum, that no-one is above the law; it applies equally to all. More broadly, I think the term implies something about the quality of the law in terms of the consent to, the knowledge of, and the respect for the law by the people it applies to. It is this broader meaning that is endangered by selectively enforced or even unenforced laws.
If the law is selectively enforced, then the statement "That's illegal" can be justly answered with "That depends on whom you know."
If the law is unenforced, which is to say it is a "dead letter," then the statement "That's illegal" can be justly answered with "Who cares?"
In either case, the law is disrespected.
The extent of the problem of unenforced laws in the UK is indicated by a 2012 joint report from the Law Commission for
England and Wales and the Scottish Law Commission. It recommended that fifty Acts should be "partly repealed" in addition to "817 whole Acts."
Any account of selectively enforced laws in Canada would have to feature its marijuana law. Twelve point six percent of the population between the ages of fifteen and sixty-four used cannabis in 2009. At some point in their lives, 44.5% of Canadians have used it. The law that criminalizes its use, in theory, makes almost half the population into criminals, and any law that is so widely disobeyed, it is fair to say, is widely disrespected. It is loved only by the police who use it to drive up arrest numbers, though few are convicted.
That is not to say that the law can be ignored safely because it can be used selectively. For example, a Canadian who had received a $50 fine for marijuana possession thirty-five years before was denied entry into the United States to watch the Superbowl.
One of the few bits of gold that glint in Ayn Rand's writing is the idea that those in power love to have laws that could, in theory, criminalize much of the population. Those laws could be taken out, dusted off, and used against anyone as convenient.
Marc Emery serves as a good example. He was a political gadfly who, besides co-founding pro-marijuana political parties, sold marijuana seeds. (Not the plant, which would be illegal in Canada, nor the leaves). Canadian authorities had been unable to stop his activities, since the selling of seeds (not plants nor leaves) was legal in Canada, and police raids were ineffective in intimidating him. Accordingly, he was arrested and given to American authorities for trial and conviction. He received a five-year sentence.
Marijuana laws, however, are not the main point of this post. It was inspired by questions I had about bigamy laws in Canada. Certainly, bigamy was regarded as a major crime when I was young, but there have been many immigrants to Canada from the Muslim countries that allow more than one wife. Does Canada let them in and then arrest them? If a Canadian with one wife marries another in a country that allows it and then returns to Canada, would he be arrested then? Could he bring in a second wife and her children under the family reunification provisions of the immigration law?
Turns out that the bigamy law, though still on the books, and constitutionally valid, is a dead letter. There have been no successful bigamy prosecutions in sixty years. In fact, the openly polygamous community of Bountiful, BC, is still in business despite the efforts of successive Attorneys General.
I believe that laws, like those against the use of marijuana and the practice of polygamy, must be either enforced in a fair and general way or completely revoked. Any halfway ground of selective enforcement gives power to authorities to persecute those who, for unrelated reasons, have annoyed the powers that be. Not coincidentally, they bring the law as a whole into disrepute.