It’s hard to imagine it at first, but last weekend’s carnage in Rio de Janeiro may actually have one positive result. It may give the world a deadline for coming to our senses about drug prohibition.

Initial reports from Rio made the obvious link with the Olympic Games, asking whether it cast doubt on the city’s readiness to host the 2016 Olympics. But that isn’t really the right question.

It’s not South American policies that have created a massive illegal industry that can now rival governments for armed resources. The policy of drug prohibition has been driven all along by Western governments, principally the United States.

Make no mistake, this is not a problem about gangs or drugs, this is a problem about prohibition: about bad public policy. Tobacco and alcohol are just as dangerous as most of the illegal drugs on the market, but no cities have been turned into free-fire zones by competing tobacco and alcohol companies.

We’ve known this for a long time, but because the worst consequences are displaced onto safely remote places, Western politicians have been able to avoid facing the problem, and continue to prop up failed policies with scaremongering about drug addiction. Even among those who know that something has to be done, it’s been difficult to muster the appropriate sense of urgency.

Now, however, we have a fixed date to work to. Rio will host the Olympics in a little less than  seven years, and it is simply unacceptable for the millions of affluent visitors to be risking the sort of mayhem that last weekend brought.

Of course, it shouldn’t be acceptable anywhere, at any time. It’s shocking that the issue even has to be put in these terms. But we know from experience that our politicians will never act as if the lives and happiness of the world’s poor were a priority in themselves: it has to brought closer to home. This just might do the trick.

That gives us seven years to make serious progress in dismantling the worldwide structure of drug prohibition. It’s a big task, but not impossible: once the momentum is there, policy can sometimes change with remarkable speed — the introduction of prohibition about a century ago is itself an example.

It’s up to those who understand the problem to keep the pressure on. The prohibitionists’ vision of a drug-free world has turned into a nightmare. But prohibition-free by 2016 — well, there’s a target worth aiming for.