Another reason why putting Avatar in Animal Kingdom is a bad idea is the message it sends. In contrast to the rest of the park's more optimistic and hopeful look at conservation and that there's still a chance that we can fix things and there's still time to fix said things, the message Avatar sends is that none of that matters because the planet's just going to die anyway and it's all our fault because of humanity's stupidity.
Yes, Avatar fits into the conservation and environmental messages of the park, but when taken within the context of the rest of the park's contemporary setting, it suggests that whatever we do to try and stop our environmental devastation, the future refuses to change.
I look at the ideas of putting Wall-E into Tomorrowland similarly because its overconsumption-based environmental apocalypse doesn't mesh with that area's optimistic look at the future at all.