The Cosmic Iguana reports FAHRENHEIT 9-11 GIVEN “R” RATING. The MPAA stated that the rating is for the film's “violent and disturbing images and for language”.
I haven't seen the film so I can't say I know this is wrong, but given the violence that gets allowed into PG-13 films — I won't take my kids to them (yet) — and the fact that the film is about what it claims are real rather than fictional events, I am suspicious. (On the other hand, Passion of the Christ got an “R” rating, and many people consider it to be all about Truth…)
Then again, if the film has, say, images of torture, do we want (older) kids to see it? Half of me says no, half of me says we should encourage them to see it.