It seems the word "again" in the post was a stupid mistake. No idea why I wrote it. Struck it out.

When humans first learned language and tool use, they couldn't breed very fast because they didn't have enough food. So using the plant would be okay for them. But if I were told today that some unknown group of humans is breeding much faster than average, I'd bet (at moderately strong odds) that they frown upon use of the plant.