because 'illegal' drugs shouldnt be illegal.
you can legally buy arsenic, or any other poison, and itd probably make you feel funny for a while, till it took your life.
but drugs that do funny things to you without killing you immediately are illegal? please mister officer.
also, im part of mother natures plan...medical science improves so that humans are no longer subject to natural laws, such as living according to the resources available to you in your environment without causing the extinction of other species.
so we take drugs and shoot each other, and thus check the burgeoning human population that threatens other species with extinction.