I agree, but have some additional points to make...
1. Regardless of whether or not it changes anyone's mind, movies of this type are still a bad thing. The only way to show "them" that is to make one of our own.
2. Whether or not people go to see the Farenheit 911, the accusations that are made within the movie will be parroted across the entire country - by liberals and media outlets (redundant, I know). The average Joe will hear these accusations and many will be inclined to believe them without doing any fact checking for themselves. It's a sad truth.
Frank Rich had a largely lauditory review of Moore's film today. But even Rich- no Bush fan- said that the weakest part of the movie were the cheap shots at Bush and going over worn out old scandal stories. Rich said the more powerful parts of the film were the ones that didn't have Moore in them at all but was footage given to him from Iraq showing an actual American combat death, the killing of Iraqi civilians by American troops, Angry wounded troops in hospitals, and a formerly conservative pro war mother reading her son's last letter home before he died in which he slams Bush for sending him there.
The anti Bush rhetoric in the movie is just standard and nothing that the media is going to get interested in. But some of those segments I mentioned could be damaging.