You have got to understand one thing.. Every damn thing has something positive in that.. Even a dead watch can show you the correct time twice in a day.. It is same thing with pot/marijuana/weed or any psychedelics.. Weed, mushroom and ayahuasca can give you a euphoric feeling and you may feel great for some time. It may even open your psychic centres for some time. They may even have medicinal properties. Agreed that they are not similar to your cocaine/meth or some other shit which are downright wrong..
However, the negative effects outweigh the positives.. Firstly, these can be highly addictive. I have seen people become so addicted that they ruin their lives. I had one colleague who had to get stoned before coming to work (can you imagine someone coming stoned to work)? Addiction is addiction, be it coffee, tea, cigarettes, harmful drugs or psychedelics. Once you are addicted, it is "bye bye" to godhood and "hello" to a hospital and rehab.. The main reason it is made illegal in almost all countries is that ordinary people don't know shit about using it for medicinal or spiritual purposes. People may think that "pot or psychedelics must be legalised", but they are living in a fool's paradise. They are fools to believe that they and every Tom, Dick and Harry knows how to use these things.. Start using them and before they even know, they will be living zombies.
Secondly, it may open your psychic centres. But if you are not an experienced guy/gal, you are opening your psych to pretty much every entity out there, good or bad.. While the good entities and our gods won't fuck around, the enemies, greys, reptilians and all the sorts of shit creatures can fuck you up. I have been reading a book about Aghoris in India. A famous aghori pretty much says that even sufficiently advanced aghoris sometimes lose complete control and fuck up their lives because of these psychedelics.
So, why in the whole damn world would you want go for these shit things? You want to have the same spiritual effects? Listen to beautiful music. Chant mantras. Involve yourself in hatha yoga, raja yoga, martial arts and those sorts. You won't have a need for any damn shit-delics.