I got turned off on Michael Moore to a point after watching "Bowling" and seeing how he totally baited Charlton Heston into doing that interview. Yes, it was a little amusing, but it's not really fair when you interview someone who is completely not prepared for your topic, and is basically more of a figurehead than a real expert anyway.
Moore is a good film maker who chooses controversial topics, but like others have said, if you're already on his side, you'll stay there, and if not, his movies won't do anything if you have any capacity to think critically.