The government's drug tsar, Professor David Nutt, has caused a furore by commenting in a scientific journal that the club-drug Ecstasy is about as dangerous as riding a horse.

He's probably right. I've seen the lives of young girls ruined through an addiction to ponies. Their minds seem to turn to equine mush. And of course falls from horses can and do kill or paralyze people – as in the case of Superman actor Christopher Reeve.

But I'm not proposing that horse riding should be made a Class A activity. (I'm sorry I mentioned that idea: it can't be long before the government starts banning dangerous sports and withdrawing NHS care from those who ride motorbikes or go mountaineering.)

Professor Nutt might have been unwise to mention the comparison, but some rationality in the debate on drugs is devoutly to be wished. When I thought that my teenage son might be taking drugs at school, I asked a neighbour, a clinical psychologist, for advice. His view was that schools were rife with drugs, but that most of them were far less harmful than alcohol and cigarettes. It put things into perspective.

It's only when we can actually discuss the real risks of drugs that we will be able to advise young people on how to handle them. But the government seems to be more concerned by the outrage of the Daily Mail than the facts. It spreads the misconception that all drugs are as bad as heroin or crack – driving the others underground and making them more difficult to control. As a policy, it's failed.

True, many modern drugs haven't been in common use very long, so it's difficult to know their full medical and psychological effects. Even with drugs that have been around for years, like cannabis, we are still learning the full physical, psychological and social consequences. So maybe we are right to be cautious about them. But let's be honest: because then, at least, we can steer people away from the most damaging drugs by giving them a genuine profile of the risks.