(This post has mild spoilers for Season 3 onwards of BSG .)
Right. We've covered the problem of comparing assuming a black person might be different to assuming an alien cat-like creature from another world might be different. Let's talk about the film in the context of the genre to which it belongs.
I can see why Sek is arguing that the film pushes the idea that it's necessarily ennobling to spend time soaking in the non-white experience. However, it is far from the only conclusion to be drawn. Yes, Sully's tutelage under Neytiri proves spiritually enlightening, but I would submit that this has nothing to do with underlying racist principles, and everything to do with the fact that the view that we could stand to stand still and sniff the roses every once in a while is a widely held one, whereas there is a notable lack of people arguing that whilst Christianity might be all very well, isn't it time someone designed a toaster that works underwater?
Taken in this context, the Na'vi are an argument that we need to redress the balance. You might not agree with the sentiment, but it seems clear to me that such is what it is. Is BSG racist because it carries an overarching theme of mankind's reach extending its grasp? Sure, there are racists in BSG, which is part of what makes it so interesting, but is the whole show racist because by Season 3 it's beginning to argue that the best idea is for Cylons and humans to skip through marigold fields hand in hand, and blow the living shit out of anyone who claims a pollen allergy? 
OK, comparing BSG to Avatar is a hell of a stretch (though in fairness the conclusion to Avatar in no way made me want to build my own race of death-dealing machines and going all Caprica City on RDM's ass), but that's only one of dozens of examples. If a sci-fi film features a race more technologically advanced than we are, then either they are also more socially advanced, and we have to learn how shit we are, or they're evil mo-fo's and the film will revolve around finding the least implausible way possible to slap them down and send them back to Vega 7 with their prehensile tails tucked between their segmented legs.
You can even swap it round entirely and have the advanced heroic humans getting boned by primitive savage alien killers, as the Aliens films prove. The point here is that the tech-level is generally irrelevant to the assignation of the heroic and villainous labels (of course, a particularly smart film can bypass that in any event, but I'm not remotely trying to argue that Avatar is particularly smart), only the faith issue determines whether the film will be about humans learning (or failing to learn) from other species, or whether we're going to need to saddle up and beat the shit out of something.
In short, then, you have four choices. A race is more or less tech-savvy, and more or less, for want of a better term, discerning in their choice of faiths and behaviour (and let's not forget that Sully didn't reject humans for Na'vi so much as he rejected indubitable twats for Na'vi plus legs plus the woman-cat-Uhura-being he loved, it's not hard to believe that frolicking through the jungle would feel ennobling compared to discussing how many more motions we have to go through before we can start neutering kitty-cats). Whilst Avatar may be a particularly blunt and moronic version of one of the four options, it is still part of the sub-group that suggests we can in fact learn things from other people. While Sek sees Sully's eventual apotheosis (hey, he turns into a frickin' Avatar) as an attempt to assuage white guilt, it can also be seen as an argument that we are better exchanging our similarities and differences and that maybe we can become better people in the midst of the fusion.
If nothing else, had Sully's ability to bridge two cultures not proven pretty damn useful, it would have been a pretty limp ending. More to the point, it would imply that to share culture would be to lessen oneself, and it's difficult to see how anyone could label that the less racist option.
Anyway, that's an awful lot of words to argue with a piece that I thought had an awful lot of excellent points to make. I guess three days of miserable gribbliness has left me hankering for endless rambling. More so than usual, I mean.
 I must confess as to a certain degree of curiosity regarding whether or not Chemie has made her peace with Felix Gaeta's unhappy airlock experience.