If people want to live like the Na'vi, they can. Move out of a city, grow your own food, recycle, give back to the land. I like fantasy a lot. I am a huge LOTR person. If Rivendell and Hobbitton were real places, yeah I would love to live there. However, I know they are not so I just read the books and watch the movies to enjoy them. I do hope the people who are depressed about Avatar get help. They need it. Hopefully, they can realize they can adopt some of the themes of the movie in their own lives and watch the movie repeatedly to enjoy Pandora.
Just as a side note, I think every movie can be offensive in some way. If you find it offensive, don't watch it.