The explanation of the Reavers never bothered me. What I really don't like about the film is how it tries to imply that River's psychoses are all the result of her knowing the Miranda secret, rather than the years of constant torture and experimentation. The Operative's line about "Judging from [River's] deteriorating mental state, I'd say we're both better off [for not knowing what she knows]" makes me cringe every time I hear it, as does River's long gaze into the camera and emphatic declaration of "I'm alright" after the secret is outed and she can, I guess, be perfectly normal now since everyone else can share the psychosis-inducing secret.
No part of that even begins to make sense to me, especially since "Ariel" gave a much better explanation for River's behavior - the fact that her brain had been sliced and diced by Alliance scientists. And if she is still crazy at the end of the film, then Mal must be feeling a touch suicidal when he makes her the new pilot.