The natives in these two movies are fictional people in fictional places, and shouldn't be taken seriously as anything but plot devices.
You're right. I made the same observation as the critic when I saw King Kong -- and I was glad to see it because what's also true is that people aren't born with a universal human understanding of compassion. It's taught. Wicked, cannabalistic, brutal, sadistic tribes did and do exist. What American Indians did on a battlefield would make Charles Manson proud. Somewhere down in each one of us' guts, we must comprehend and learn to fear the fact that such soullessness as human sacrifice, barbarism, and slavery are the natural state of man without God. Sooner or later, it's going to have to be recognized that Christianity plays a unique role in better futures.
Again, this is the reason it's going to be a long war.
This seems to be the thread that ties all of Gibson's films together.