Violence and intimidation is used rather than advertising to promote products and distribution. Criminalization also creates a disrespect for the law. It is also the major source of police corruption. Bill of Attainder. Legalization would allow the government to regulate, tax, and better control production and distribution of drugs.
Some drugs are clearly more harmful than others.
They can still be regulated legally. The two most harmful drugs in terms of illnesses and death are tobacco and alcohol. They are regulated. Even if drugs are not legalized, penalties for use could be changed. Marijuana may be most controversial drug.