You have to write with conviction when you write about the things you believe in but I agree with Roxane Gay, who is such a generous writer, that your argument is much richer if you allow yourself to take in your opponent’s perspective. Here she is being interviewed in Art Talk:
NEA: I recently read an interview in which you talked about the sense of surprise you felt with An Untamed State when you realized one of your characters was more central to the story than you’d initially thought. Do the same sorts of surprises happen when you’re writing nonfiction pieces?
GAY: In nonfiction the surprise always come when I come to the realization that I’m not as right as I think, that the other point of view is as valid. I think that we get so defensive and deeply entrenched in our arguments that we forget to respect the opinions of others. So, for me, it’s always a valuable surprise to see [where the other person is coming from] even though I disagree, and I can try and acknowledge that respectfully
This is similar to Dennett’s guide to successfully composing critical commentary .