As drugs are illegal, they are being marketed by outlaws, who charge an inflated price for them. Much more inflated that the amount it requires to grow, manufacture and distribute them. As a result, there is a growing black market for the distribution of drugs and drug users eventually need to commit crimes like theft and robbery to support their habits.
The average crime rate in the U.S increased twice fold due to the prohibition on Alcohol. Once the prohibition was lifted, it decreased back to its original state. It is expected that drug-induced crimes cause a similar increase, due to the similar nature of this prohibition.
In this analysis one should also include the very “crimes” of drug use, trafficking, and sale, as well as crimes caused due to the criminal nature of some drug dealers. Drug trafficking is also a huge source of income for Organised crime.
All of this crime can be eliminated in a swift blow by legalising drugs. When drugs will become legal, they will be produced, distributed and sold by local legitimate entities, who will be subject to Capitalistic market constraints. Their prices will drop to a minimum, allowing everybody to buy them at the needed quantities. Criminals will no longer be able to make a decent living from selling them in the black market (as there will be none.).
Law enforcement organisations attempt to stop drug trade by catching drug shipments, and drug dealers. However, any shipment or dealer that is caught, has only one effect: a temporary increase in the price of drugs at the location to which they were intended. Most drug shipments and transactions are never stopped, and it is a pointless struggle to try to stop them.
Illegal drugs are not sold in the free market and as a result the sold good is subject to the whims of the local outlaw manufacturer or distributor. As a result, they often have reduced quality, which can cause a lot of unnecessary health side-effects on their users, including many deaths.
During the prohibition on alcohol it was observed that the quality of alcoholic beverages has heavily decreased, and the same thing happens now with the currently illegal drugs.
Since it is hard to find high quality drugs, when drugs of a high quality are found the drug user will buy as much of it as they can afford, especially if it's a good deal and therefore they will have a much larger quantity around than they normally would have and therefore tend to consume more drugs.
Imagine that liquor fluctuated in price and quality. You go to the store and sometimes there are harmful chemicals in the liquor, sometimes the prices are extremely high, sometimes there is no liquor at the store at all. Only once in a blue moon are prices very good and quality good (say, it only happens once a year). In that case, you would buy as much as you could afford. Naturally, people who only use alcohol might not agree with this, but that's because they have never been in that situation, since alcoholic beverages are fully legal.
People who become heavy drug users often need to find a way to finance their habit. As a result, they often become drug dealers themselves, and try to push drugs onto other people, including children.
Furthermore, once they become dealers, they become exposed to an even wider variety of drugs than before, and they are likely to try drugs that they never would have before because drugs are essentially free to them. And a great way to push drugs on people is to consume drugs with them. So, to make more money, they end up consuming more drugs.
Making drugs legal will stop this vicious cycle. The price of drugs will drop to free market levels, and people will not need to become drug dealers themselves to finance their habit.
Drug dealing in a society where drugs are criminalised is a way to make a lot of money. As a result, young people among the poor find selling drugs an easy way to earn their living and escape the more demanding path of working in an honest job.
This causes a bad effect on the societies in poor neighbourhoods, who turn to drug dealing instead of advancing their rank in the honest world. Making drugs legal will kill this easy way out, and force the young people of the poor to struggle for a honest living and gradually advance their personal and collective financial status.
There is a common pattern in history of “unholy enemies” - groups of people who are presented by leaders to be of such evil nature that the general populace should be willing to sacrifice their lives, freedom or well-being to fight them. These have been the Jews in Nazi Germany, and the Kafirs in Islam. In modern society, drug users now serve as an unholy enemy for which the government can undermine Liberalism and gradually repress the people.
Yet, drug users are no such enemy - they do not pose a threat to society. Plus, they are people in need of help, not in need of being hunted and prosecuted.
The legalisation of drugs will put a stop to the irrational trend to make drug users an unholy enemy and for the government to undermine the individual rights of the citizens. There is no good reason to undermine individual rights, much less one that is useless and pointless as trying to “win” the war on drugs.
Since drugs are illegal and using them can jail a person, drug users usually exhibit abusive behaviours: they lie, steal, and become dishonest and suspicious. This is not an effect of the drug itself - it’s a result of the psychological and legal situation in which they are present. By legalising drugs, one can be sure that drug users will be able to openly admit their problems, and seek help.
Drug users tend to associate with other drug users, because non drug users do not understand drug use and have a preconceived idea that they are intrinsically bad. Therefore, drug users are always around other drug users, and likely always around drugs, and therefore tend to do them more. When breaking a habit, you must stop your enablers, but drug users eventually mostly have other drug users as friends, so it is very hard to break the habit of drug use even after it becomes a problem. That is because they are always around drugs and other users and it takes a large amount of will power to refuse taking drugs when one is around it all the time.
As a result, drug users form a subculture. The drug user ends up alienated from his or her non-drug using friends. However, the cause is not the drug or the drug problem, it is the illegal stance society takes on drugs. One is a criminal if they possess drugs, so they will not do this openly, yet they can do this somewhat openly among the drug-using subculture, and possessing drugs in that subculture makes you high status in that subculture. Drugs and especially good quality drugs are of a higher value in that subculture, than being rich.
The prohibition of illegal drugs prevents some legitimate uses of the plants from which they are made. The most prominent examples are paper that can be made out of Hemp, but is now made out of cut-down trees instead (which is certainly not good for the environment), and the various medical uses of Marijuana.
The prohibition on drugs puts many people in Jail - there are over 1 million prisoners for drug offences in the United States. There are even more if we consider drug-induced offences such as drug-induced theft.
These prisoners are a large strain on society which needs to support them. They also prevent more serious criminals from being jailed, which undermines the punishment and rehabilitation system of the government.
The legalisation of drugs will free the prisons from false criminals, and restore justice. And the lawful people will no longer need to support hundreds of thousands of jailed drug users and dealers.