Oh come on, Bob. The 'they're mercenaries' excuse is a paper-thin cop-out and you know it. If Cameron really wanted to hammer home that specific fact, he would have actually gone into some detail as to what the hell said corporation actually does, how it amassed enough money to create its own space armada, and where the bulk of their mercs actually came from. I'm assuming that the majority were former soldiers.
Granted, the Na'vi were made out to be pretty aggressive when necessary too, but it just seemed that Cameron was weakly trying to cover up the anti-military message with his even stronger anti-corporation message.
That's the thing that pained me most about Avatar. It had the potential to be the perfect moviegoing experience. The visuals, setting, and CGI were all absolutely stunning, but I hated the story and the characters so much that it got in the way of me truly enjoying it. You said a more involved story would distract from the overall experience, but I strongly disagree. How it looks is important, but unless the story's good and/or the characters are well characterized, I just can't get into it.