The story was really generic. I'm surprised so many disagree.

Right? Another blockbuster movie openly advocating for eco-terrorism against the American government? Yawn. When will they finally think of something new?

I don’t get it. The government invaded a sovereign world and they don’t have the right to fight back?

Edit: I can’t find this talking point on the internet in the usual places anywhere.

I don’t see anyone saying they don’t have the right to fight back. That’s why it’s an interesting story for me, it shows why eco-terrorism can be a rational answer. Also fun to compare avatar themes with his ex-wife’s film that came out the same year, zero dark thirty.

Is that exactly what the person I replied to was complaining about?

I think the person you replied to was being sarcastic. They were pointing out that the ideas presented in the movie are anything but generic for major blockbuster movies.