Regardless of whether I agree with the parent comment, I'm inclined to agree that it shouldn't be downvoted. Even if the opinion itself is inflammatory to some, it seems to be expressed in as conscientious a way as possible, and the reasoning (whether you agree with it or not) is explained. You could certainly argue that there are flaws in the logic, lack of evidence etc., but IMO it does at least add to the discussion. If unpopular opinions are regularly downvoted, people will stop expressing them, even in the cases where they might be right, or at least useful to the discussion.

I really like the metric that downvotes should be for comments that are uncivil and/or don't add anything of value to the discussion.