Moore's lack of "honesty" tends to make his message less "credible" in my mind too. But, in the end, he's trying to get a message across. If he were to tell a bland, cold documentarian style story regarding these issues, (1) they wouldn't be as controversial, which is the true life blood of his work, and (2) people woudl be bored to tears, and never go see his movies again. I think that it is a testament to his work that he can make people (a) laugh, (b) think and (c) make a point. Whether I agree with his views all the time are another issue. Whether I wish that he toned things down more so that his "good" messages coudl be taken more seriously - again, that's a different issue.
On the whole, Moore's style has made him a household name, and maybe the only documentarian (used however loosely as you prefer) that people can name without too much thought.
