David Nutt, along with many other leading scientists, published a study a few years ago that showed how the overall harms associated with some legal drugs, such as alcohol and tobacco, dramatically exceed the harms of some illegal drugs, such as cannabis, ecstasy and LSD - and even the harms of heroin and cocaine.
Of course, these top scientists were right, but politicians continue to ignore scientific advice, and society continues to be largely in favour of current drug laws.
Here are three factors that might explain this paradox:
1. Capitalism and class
Noam Chomsky, an American social critic and political activist, offered some interesting arguments to explain how capitalism and class shape the legal status of drugs.
Cannabis, for instance, is a plant that can be easily grown in someone's backyard, so it is not as easy to commercialise for profit.
Tobacco, on the other hand, needs industrial technologies and hence is a suitable product for commercialisation.
Similarly, making high quality alcoholic drinks - a fine wine or a decent bottle of whisky - is not nearly as easy as growing cannabis or magic mushrooms in your garden.
It can be argued, however, that the recent US experience with cannabis legalisation has shown that it can be successfully commercialised, but let's not forget that commercialisation of the plant was one of the major arguments used for legalising cannabis in many US states.
Drug policies can also be used as a tool for "social cleansing". Governments will ban drugs that are associated with poorer people, such as cannabis. This will fulfil a common goal by the elites of selectively isolating lower classes.
For example, governments can sometimes find homeless people to be a nuisance, and banning drugs such as cannabis would provide a legal excuse to get rid of them.
During alcohol prohibition in the US in the 1920s, the government made an exception for whisky, a more expensive alcoholic drink, which you could buy with a doctor's prescription.
This ensured that those who were poor could be locked up for drinking alcohol, while the elites could legally obtain the drug if they wanted to.
2. Poor understanding of risk
We overreact to immediate threats and under react to long-term dangers. This is a well-known phenomenon that was described by psychologist Daniel Gilbert of Harvard University.
A person will generally perceive a 14 percent risk of developing lung cancer from tobacco to be lower than the 0.01 percent chance of immediate death following the overdose of a party drug, such as ecstasy.
In statistical terms, though, you are more than a thousand times more likely to die from using tobacco than you are from taking ecstasy.
This human ineptness in perceiving long-term risks is revealed in our attitudes to the impending doom of climate change. Because the most serious consequences of global warming are still decades away, many people are apathetic towards its threat of wiping out the human race.
The same people might nevertheless overreact to the danger of a terrorist attack that could result in very few fatalities in comparison.
3. Confusion between effect and toxicity
We can easily think that the more obvious the psychological effect of a drug, the greater health risk it poses.
We have evolved over millions of years to associate sudden and unusual psychological changes with fear. Unusual mental states serve an evolutionary function: they warn us that something is not quite right.
The effects of alcohol and tobacco are very subtle and gradual in comparison to, say, LSD.
It is, however, difficult to realise that the extreme mental transformation caused by LSD is independent of its effect on your health.
That is because the change it creates is a direct result of a safe modification in neurotransmitter levels in the brain, not an indirect change that is meant to alarm us from a physiological malfunction.
Of course, social attitudes to things like drugs are extremely complex and can never be reduced to a finite number of reasons.
The above is speculation, but being aware of some of the reasons that affect our social attitudes to psychoactive drugs will hopefully help us fight for more rational and less harmful drug policies and laws.