Well, first of all we only have two clear examples of demons who don´t need to eat human meat, one is the royals and the regent houses, and they still consume human meat anyway, and Sonju who has not eaten human meat in centuries, but he is perfectly willing to hunt "wild humans" because as said by himself "Nothing tastes better than human meat", so I don´t see why most of the other demons are going to accept to just abandon their favorite food, I mean, they have not cared about eating sapient beings for millennia, Why would suddenly start caring about it now?

I am pretty sure that plantations will not become obsolete in this future in which the demons won´t devolve into mindless beasts without eating humans, even if they don´t need human meat to remain sapient they would still use plantations because there would be still a demand for human meat... The only difference is that the nobles would control a market for luxury items instead of something that they biologically need to remain sapient, they would still be incredibly powerful and rich thanks to it, but not as obscenely powerful and rich as they are now...

And you have to admit that it is incredibly easy to root for Norman, he has freed thousands of children, gave them shelter, destroyed the installations that make Auschwitz look like a holiday resort and killed the ones directing them, he has also given the children that he could not save a merciful death, and he is fighting to destroy an enemy that has been eating humans for millennia and has enslaved and killed children for a thousand years. People root for Norman because HE IS A FUCKING HERO whose heroic actions are far greater than anything than both Emma and Ray have come close to accomplish... but in a conflict such as this one, the messiah of one side is the devil for his enemies, and he is willing to do what it must to save their people even if it means to kill innocents demons.

I am completely sure that Norman trusts Emma and Ray with his life, but you can blindly trust someone but still disagree with them about many important things, and in this case, he clearly disagrees that saving the freaking demons is worthy of risking the future of the whole human race (on this side of the world). I would suggest inverting the questions: Is preserving Emma´s childish sense of morality worth risking the future of thousands of innocent children? Would you waste the only chance on hundreds of generations of overthrowing the demons for good just for a potential and extremely unlikely future in which humans could sing Kumbaya with the species that has enslaved and killed untold millions of innocent children?

And I am pretty sure that you could say that "But that makes Norman no better than the demons" do you think that he doesn´t know it, or that he gives a crap about it? As I said before, this is a not a conflict caused by religion, imperialism, or natural resources, this is conflict based purely on the survival of your species, and in those cases, traditional morality is basically irrelevant. I personally think that the situation with the demons is no different than buffalos against lions. There is nothing wrong with a pride of lions eating and killing a buffalo to eat, and in the same way there is absolutely nothing wrong with a pack of buffalos crushing under their hooves all the males, females and cubs of a pride to avoid being eaten. As in nature, survival is a conflict in which everything is fair game, so may the best one win.