> humans never ate until within the last ~50 years

Humans have been eating some of these for thousands of years. I know "extract" is a scary big scientific word, but most of the time it's just immersing the grain in hot water, strain it to remove the pulp, then boiling the liquid to concentrate it. You can separate the starch and protein from any bean or grain in your kitchen with some basic kitchen equipment and hot water.

The dose makes the poison.

People weren't doing that at a mass scale before people figured out they could make money by increasing addictiveness, once technology was good enough.