The human animal survives due to cooperation. An individual human is weaker than a lion, slower than a jaguar, cannot fly, has very small fangs and does not have the weight of any of the large beasts. Despite these, humble, limited abilities our species has adapted and spread to every continent in the world - more than any other species.
This is because of a human ability to work, solving complex problems as a group, despite being individuals. When individuality is put aside for the quality of the group effort, a group may experience "group flow". In group flow, the members of the group can usually correctly anticipate each other's actions which creates an effective and efficient functioning of the societal machine.
Drugs, it is perceived, create unexpected behaviours, and therefor reduce group flow. The demonstration of unpredictable behaviour on the part of an individual is viewed on with contempt and criticism on the lighter side or with suspicion and fear in the worst of cases.
Because of the "unpredictable inebriant" many societies today ban drugs. Drug legislatures are often emotional reactions to aberrant behaviours that are, or are perceived to be the result of drugs.
However, we can address our ignorance as to how our behaviour changes under the influence.
We can test, measure document and prepare for, behaviour under the influence of drugs.
If drugs, and the behaviours they induced were studied carefully, they would become predictable and society would feel comfortable with them.
There is also, in my opinion another inherent flaw that society sees in taking drugs recreationally.
In the absence of drugs, one must change reality and please his peers to achieve a sense of well being. The just reward of feeling good comes from the labourer's endogenous neurotransmitters, secreted or fired as a result of their or others being happy with what she's done.
With recreational drugs, however, the reward is the consumption of the drug itself without any improvement paid to the environment - be it physical or social. This often leads to a "drug centric" lifestyle which ignores any traditional values no matter how important because they do not play a role in conferring pleasure.
For these two reasons it is clear that the architects of society would like to write recreational drugs out of the standard narrative. Being the social animal that we are, we are sensitive to irregularities in other people's behaviour more than we are sensitive to the weather, or other external conditions. It is this sensitivity which sparks the war on drugs everywhere there are people. We must simply observe that prohibition leads to ever increasing problems whilst regulation leads to tolerance and functionality.