Really? Have people consumed so much lack of common sense kool-aid that they believe humans know better than the Earth? From a purely birkenstockian point of view, it should be obvious that these naturally occurring things are there to help us. Why else would endless species of plants/fungi/etc. happen to be hanging out at our feet?
The mistake we've made is that we're too skeptical. Instead of believing in what's right in front of us, we choose synthesized drugs and the ideals of people no more keyed into existence than you or I.
Be aware of what's around you and learn about why most of what they say is harmful or "illegal" isn't and shouldn't be. Start with marijuana.