The thing about Moore is that he presents valid evidence, and shocking sometimes and jumps to conclusions using clever interviewing and powerful music, incriminating clips etc. The reason why people say farenheit 9/11 is a piece of bias is because you have interviews with idoit soldiers and footage to make it seem incriminating. Like for instance, Moore uses the power of language very well.
Who noticed in the opening scenes of F 9/11 that Moore says ' They pelted bushes limo with eggs' , and the footage shows only one egg hitting the car, and that is probably all that was thrown. His wording is the key, because it makes it seem like alot more. As i said earlier, he presents valid evidence and shocking footage at times, but he uses these to blow up something that people shouldnt get so excited about. He just plays situations and makes them very intense.