What is the optimum number of migrant deaths? The answer is not zero.

Think of this from the point of view of UK voters. They want tougher immigration controls. But these impose the risk of death upon migrants. If people can't enter the UK legally and safely, some will try to do so illegally - and this will sometimes entail taking risks by travelling in containers or unseaworthy boats.

I suppose it might be technically possible to have fully secure borders which do not impose a risk of death upon migrants - say, if all lorries and boats entering the UK are searched before they set off - but doing this would be prohibitively expensive. Feasible border controls invite some migrants to risk death by using dangerous routes.

It might well be rational for some migrants to incur this risk. They must weigh the costs of trying to enter the UK - which include payments to traffickers as well as the risk of dying in transit - against the benefits. If the latter are high enough - as measured by expected wage differentials or the risk of death or imprisonment if they stay in their home country - then it might be rational to incur a risk of death in transit.

Just as the criminalization of drugs generates risky behaviour among drug users who take drugs of unknown purity and composition, so the criminalization of immigration generates risky behaviour among migrants.

But let's be clear. Such risks arise inevitably from preferences and technology: the preferences of voters to restrict immigration and of immigrants to come here; and the imperfect technology of border controls which leaves open some dangerous routes into the UK.

There's an analogy here with the economics of crime. Just as there is a (positive) optimal amount of crime because the costs of completely eradicating it are prohibitively high, so there is also an optimal number of migrant deaths.

From this perspective, it makes no more sense to mourn the death of a migrant than it does to mourn the arrival of a restaurant bill. Both are the inevitable result of our choices. Such mourning would be sanctimonious hypocrisy - and voters and politicians would never be guity of this, would they?