The key is this: Substances such as LSD, psilocybin or DMT can put the brain into a special mode of functioning which can in turn enable capacities which can be described as "psychic" in certain circumstances (this is also linked to the "mystical experience" which is often mentioned by users). These experiences make people aware of the fact that there is a whole invisible world (or spiritual dimension) which has nothing to do with our material experience. This understanding leads to a much higher degree of freedom for the person experiencing all of this. For obvious reasons, such a person can be much less manipulated by negative emotions such as greed, hatred and fear. It leads to less war and less consumerism. But both of these components make up big parts of the US economy, which represents a small percentage of very wealthy people who are afraid of losing their dominance. This is probably the most important reason why these substances which have so much potential have been suppressed for so long, without real and valid justification.