L. Ron Hubbard says that to be "pure," "credible," and "have a point," (all things he clearly values highly) science fiction must be plausible; limited in its possibilities; have to do with material-based sciences; be focused on people over machines; and not incorporate spiritualism, the supernatural, mythology, or similar non-materialistic phenomena or notions.
Does Battlefield Earth meet Hubbard's own criteria for science fiction which is not just "pure," but credible and pointed? The story seemed neither plausible nor limited to me, but it's been a very long time since I read the novel and I'm willing to be convinced otherwise by people more familiar with it than I.