Was an excellent herb to our fathers of old."
The earth is kind to us. There's not much that grows in the wild we can't eat. We can even eat grass as Nebuchadnezzar did. It won't do us much good but it won't kill us either. The things we absolutely shouldn't eat have a way to letting us know we should leave them alone. Fly Agaric, for instance, with its bright red parasol and white spots isn't something you're going to ingest by accident. There are no absolute rules but mostly if a plant looks nutricious, it will be. And even the poisonous things- like Fly Agaric and Digitalis have their uses if handled wisely. Fly Agaric will carry you off between the worlds and digitalis will regulate your heart for you. More often than not the thing you don't actually want to put on your dinner plate will serve you in small doses as a magic or a medicine.
There are those that argue we went wrong when we gave up being hunter gatherers and started to farm. Farmers eat a less varied diet- and I believe there's archaeological evidence that the early ones had worse health and died younger than their free-ranging ancestors. Again, once you start enclosing land you create opportunities and excuses for war, oppression, theft and all sorts of reasons for not loving your neighbour, also employment for lawyers. The story of the garden of Eden seems to reflect this change.
We haven't lost the old knowledge, only neglected it; there were always those who knew it- witches, medicine men, herbalists- some of whom wrote books. It exists for us to rediscover- if we so choose.