Dissenting from your opinion in what I hope will be a civil, constructive manner, I agree with you that once in a while I get downvotes solely because I am expressing an unpopular opinion. But that is rare. And I don't shy from expressing minority opinions here on several issues. I don't get a large number of downvotes at all. My two comments with the largest net number of downvotes were (to me, in hindsight) comments that I could have written more clearly with more effort at relating them to the main concern of the thread and adding new information to the thread. On the whole, I think most downvotes are adding quality of expression to the site rather than subtracting opinions from the site. There are a lot of strong opinions here, not all of them in unison, and a lot of those opinions get expressed here.

By the way, it's an EMPIRICAL question whether downvotes or posting disagreeing replies does more to discourage expressions of certain opinions. It seems to me that someone thin-skinned enough to cease posting his opinions because his comments get downvoted (rather than reconsidering how he comments and seeing if he can improve how he comments) might be just as discouraged from posting minority opinions if he sees a lot of replies that disagree with him. If a person has courage of his convictions because his opinions are based on evidence and careful thought, there is little reason not to come back here and express the opinions, even if his comments don't get a huge number of net upvotes.