A very powerful movie with one troubling flaw: Precious

I liked "Precious" (and I know I'm supposed to say that it's based on the novel Push by Sapphire) much more than I thought I would. I remember reading Push (source of the film Precious directed by Les Daniels) when it came out and thinking it was kind of melodramatic and tendentious, if well-meaning. Turns out it was a great source for a movie. Precious really throws you right into the strange and sad and terrifying world of the young girl's life: school where she tries hard but can't succeed, home where her mother is a cruel tyrant, social agencies where she's enmeshed in bureaucracy, a new alternative school where it will be a struggle for Precious to fit in. And yet - things do work out for her, in a sense, but in no easy way, it's a constant and for the most part completely believable struggle, as she gains her freedom from the horrible mother and gains a bit of self-confidence, prepares to move forward with her life. To the film's great credit, we begin to understand the mother, too, and for once a movie doesn't blame everything on the unfeeling social workers and the crushing bureaucracy of the system. The social agencies do help, and Mariah Carey, surprisingly, is terrific as a thoughtful but tough social worker. The scenes in the classroom are a bit derivative, think Freedom Writers and probably a dozen other films, but the violent confrontations between Precious and her mom are unprecedented, and the Precious's interior monologues are poignant and revealing. Great acting by Monique and the Oscar winner (name?) who plays her mom. I can understand, however, that this film is particularly disturbing to black viewers (in the same way that A Serious Man disturbed me and other Jewish friends), in that the black characters, except for Precious, are pretty much all horrible and the sympathetic characters are white or mixed-race (and the comic characters are Hispanic?). I wish that hadn't been so; it's a troubling (and avoidable) flaw in an otherwise very powerful movie.