We all want to ban something. It is a staple of our political culture. All of us are perhaps one moment away from seeking to ban what someone else is saying or doing. The nod-a-long responses of "it shouldn't be allowed" or "there should be a law against it" are the common solutions to many perceived problems.

However, to "ban" something is not actually to eliminate it, whatever "it" is. The "it" is not extinguished; the "it" may just be attended by some different consequences. The legalistic prose in a solemn document is not some magic spell which banishes horrors by invocation. To say there should be a law against a thing is often no more than saying there should be a spell against it.

In fact, "banning" things often creates new problems. In its correct legal form, a prohibition establishes certain legal and coercive consequences should the prohibited act occur: a court order for damages, say, or a prison sentence. Being banned does not thereby stop the thing from happening. It just means that the legal system will be engaged in a way it otherwise would not be.

Moreover, in the complex "real world" of ever-changing and shifting political, social, and economic relationships, the general prohibition (and the coercive sanction) can sometimes only make unwelcome situations more complicated. Some behaviour may well be discouraged (the deterrence effect); but other behaviour will be modified so as to escape detection. Or, the behaviour may carry on as before, but worsened by the criminalization of all those involved. The easily satisfied will have their "ban" but the effects may be unfortunate or unpredictable.

This is not to argue for libertarianism, still less anarchism. It is instead to urge sensible and balanced law-making. There is a positive and essential role for prohibitions and coercive sanctions in our polity. However, such laws should always be made and implemented with anxious scrutiny. Enacting the prohibition is not an end in itself. There should be regard both to the likely effects of the "ban" and to the interferences which will be made to other values important in a liberal society.

So those calling for something to be "banned" should therefore ask two simple questions. First, what will the prohibition do in respect of the undesired behaviour? And second, what other consequences may flow from the prohibition? Good answers to both these questions will inform the political choice as to whether such a ban should be implemented and, if so, how. We may even get better laws as a consequence; we could even get prohibitions that actually work and are proportionate.

The call for something to be "banned" should be the start of a mature and constructive political debate, and not the end of one. Perhaps the time has come to ban just banning things.

David Allen Green is legal correspondent of the New Statesman. He also writes the Jack of Kent blog and for The Lawyer.