I would say that first encounters of humans and entheogens were pure chance — folks picked some unknown herbs, ingested them, maybe they cooked them beforehand, or some of the herbs fell into the fire and they inhaled the smoke.

I agree that when these ancient people pinpointed which plant makes them see things, they approached them with appropriate amount of reverence and respect. No wonder, because most of those plants are certainly not for entertainment and death from overdose is not that uncommon (ergot, fly agaric, various breeds of nightshades, etc.). It really takes guts to overcome the fear and willingly go on the journey — definitely a domain of the crazy few (aka later shamans).

Then again, I can vividly imagine that Cannabis or Psilocybe were used widely by the whole community even as a part of recreation and fun around a campfire. Exactly as alcohol later.

Also, it seems to me that when we talk about early communities talking to god(s), embody animals and similar stuff, we tend to imagine that those folks took all those things literally. My personal take is that they were merely highly metaphorical and simply expressed their experiences in the language that reflected their "inventory". How would ancient animists express that e.g. hemp as a plant has a certain mental character? I bet they would talk about hemp spirit.

All in all, I don't think our ancestors were idiots who jumped to conclusions and invented non-existent entities to blindly believe in. That was a later work of people without direct experience or without actual understanding, who merely parroted inherited knowledge as tradition.

I think, we should really give our progenitors, the ones that were the real trailblazers and were by the way very pragmatic and (for obvious reasons) down to earth people, more credit.