Calling bullshit on that one Cameron.
If anyone is a role model in the film, it's Grace. She's a strong, intelligent woman who displays more compassion and understanding than almost anyone else in the film. What negatives is she incurring by spending time in her Avatar body that Cameron claims to represent an online or gaming persona? If smoking is the only one, that is by far the smallest issue at stake in the movie's world.
And she's not an aspirational role model to children? She's shown to be a great mother figure IN THE DAMN MOVIE. She acted as a schoolteacher to a ton of the alien kids and they clearly adore her, and cling to her every time they see her and she cares for them equally in turn.
Also, we're supposed to see spending time in an Avatar as a negative thing? I might have been reading this wrong, but I'm pretty sure the audience was supposed to think that the main character spending enough time in his Avatar to learn the ways of another culture, integrate with them, and therefore save the WHOLE PLANET was a good thing.