Yeah it sucks and I'm not immune to the argument. Hopefully we'll figure out cheap good lab meat and smarter animals can go back to just being eaten by bears and lions. Not much better but we won't have our guilt.
You're making many assumptions here. "Lower" intellect animals couped up in an area almost exactly the size of their bodies will still feel pain and indescribable muscle fatigue in the same way we would. It's akin to saying it's morally allowable for a highly mentally incapacitated human or a newborn to have extreme discomfort or active pain inflicted upon them because they can't understand their environment.
Foe grais should absolutely be completely banned. I would hope than anyone with a shred of human decency that knows what the duck endures abstains from consuming it.