Who is the true human?

There's been an interesting discussion going on at the Boar's Head Tavern (link) about Avatar, and particularly one of the lines, towards the end, which concerns the actions of the main character, Sully, who arrives with humans who have come to a planet in a faraway star system, and are engaged in what amounts to genocide in order to obtain the planet's resources. He turns his back on them, and indeed takes up arms to fight for the native inhabitants. The line comes from the belligerent, gun-toting, survivalist colonel who heads the soldiery department, and he asks Sully, 'How does it feel to betray your race?'

I watched the film last night, and afterwards asked a friend whether she thought that Sully really had betrayed humanity. (Her answer amounted to 'Obviously,' so that was me told!) Reflecting, I realised that really the question it raises is: Aren't the real traitors to humanity the ones who are engaged in genocide?

Ah, you may say, but we're the experts at genocide: plainly they haven't betrayed their humanity. I wonder. In a sense, are we not all traitors to our humanity already? We all know the feeling of an 'ought', a moral purpose, which is far higher than the 'is' of our actual behaviour. In siding with the aliens, Sully is being truer to the 'ought', while the miners and soldiers are being truer to the 'is'. From the perspective of the 'is', behaving in line with the noble 'ought' may look like treachery, but hasn't the real treachery already taken place?