Correct me if I'm incorrect but as far as I know greens are as bad as meat for humans, right? I mean, one of the main arguments against meat is that is bad for the body due to some chemical process after the death of the animal but vegetal stuff is hard to digest and a human never is able to fully digest it, even some people have a hard time with fruits.
I wonder why people can't just accept we suck at eating anything and that pretty much we eat what we can.

humans are omnivores. we gave up the ability to fully digest anything perfectly well in favor of being able to digest pretty much everything okish. We are the jack of all trades, master of none of food.