I think that criticizing Moore's documentaries and calling them propaganda is shortsighted.
All documentaries, with the exception of nature/discovery channel-style ones, are just a pretty word for propaganda. They all edit heavily to skew quotes, images, statistics to support the point of view they're trying to sell. Moore is no different in doing that than anything that's being put out by any 'documentary' or even the media, ALL the media. At least, all the media I've seen.
The popular press is terribly uncritical, it's atrocious, really. Everything post-9/11 was an unrepenting parade of how wonderful and strong we are and we can do no wrong and anyone who questions us or disagrees is anti-american or an enemy. And this followed through right up to Iraq. Then the public's taste started changing, and the media picked up on it. And now it's been a great big "I told you so" fest that shows only the explosions and instability with minor stories about the steps forward towards some form of stability and normalcy.
The indie press is no better. It's so obsessed with opposing everything that the "mainstream" or people in power do it tends to overlook whatever would put holes in it's stories.
I don't know Moore personally, so I really could say whether or not he's "anti-American". But I doubt it. From what I've seen of him and his movies, which is really very little, he just seems very critical of certain views, namely republican ones, but it certainly goes deeper. I think that Moore does disagree with certain aspects of American culture, as should all people, as good as it is, it's not Eutopia. But I think that he's smart enough to know when to make a controversial documentary about the right topic to get money and fame, and draw attention to that point.
All media presents it's facts with a skew in the intent. Your job as the educated consumer is to filter the facts from the politics. The best propaganda is based entirely on truth, but presented in an inflamatory setting. Until the media becomes a critical, thought provoking body without a bias, you cannot make an honest attack at any documentary (or documenterer), unless you do so from a neutral, unbiased footing, which is not easy ground to find.