Many folks who otherwise agree with most other Libertarian ideas are aghast at the suggestion that we end the war on drugs. Prohibition will reduce the availability of drugs. Illegality will deter some potential drug users. Whether, and to what extent the above goals have been achieved is uncertain.
Illegality drives up the price of drugs, making using drugs very expensive.
Many drug users resort to selling drugs to support their habits. This inspires some to encourage drug use among other potential customers, including children. Math errors can be fatal to the purchaser, and victims of bad drugs have no recourse in courts. Most drug overdose deaths would be prevented if drugs were obtained from pharmacies. The huge profits in the illegal drug trade have attracted organized crime and violent gangs.