I'll disagree with you in part while agreeing in part. I invite onlookers to apply the rubric from pg's essay "How to Disagree"

http://paulgraham.com/disagree.html

to rate how well I do in disagreeing here.

You write, Here on HN, however, as with most communities where you start to recognize the regulars (tptacek, raganwald, etc), "trolling" is redefined to simply mean "going against the grain."

I disagree with this, because I have openly disagreed at least with tptacek, and certainly with other users who have higher karma totals than I have and have been on Hacker News longer than I have, and yet I have never been hellbanned. I have seen even more open, pointed, and frequent disagreements with some of the "regulars" here from some of the other regulars, but those accounts are still alive and well. I have used the same username here, and only this one username here, during all the 1122 days since I formed my user account. To the best of my knowledge and belief, each of my posts has been visible to users since it was posted, and the majority of my comments have stayed above 0 net karma ever since they were posted.

I agree with you that expressions of opinion that disagree with the joint opinion of the most active HN participants can result in individual net downvotes of comments. Before I got here, it was declared that the site founder is okay with participants downvoting to express disagreement with comments,

http://news.ycombinator.com/item?id=117171

and when I lose karma on a net basis with a particular comment, I look at how the comment was written, and think about how I could make a comment that disagrees with prevailing opinion be more persuasive the next time. (Another user who has replied to you reports experiments in doing this, and I will look at the examples found in the past comments by that user to see how it is done.) Once in a while, if an issue is important enough to me, I'll openly (and, I hope, respectfully and thoughtfully) disagree, and figure that such occasions when I burn through karma is what karma is worth accumulating for.

To sum up, I agree with the proposition that some comments here are downvoted solely to express disagreement. The art of writing comments is to figure out how to express disagreement and still appeal to disagreeing readers as a thoughtful participant in intellectual discussion. On the other hand, I don't think most users here flag comments for disagreement, but rather for blatant violation of the site guidelines. I disagree with the proposition that anyone has been hellbanned solely for posting comments that are in factual disagreement with majority opinion here. I see plenty of live accounts that manage to openly express disagreement frequently, and I possess one.

AFTER EDIT: I note, entirely with amusement, that this comment is bouncing up and down in karma score just now. Whatever, I'm just trying to point to some reasons to think about the issue differently from the opinion expressed in the parent comment. Whether you the reader agree or not is up to you.

AFTER FURTHER EDIT, RELATING TO COMMENT REPLYING TO THIS COMMENT: Thank you for your reply. I agree that it is logically correct to say that pointing to accounts that survive despite disagreement is not an airtight proof that no accounts have been hellbanned for disagreement. On the other hand, my general point is that I don't see any affirmative evidence for the extraordinary claim that this site is moderated with swift and frequent hellbanning for disagreement as a routine part of the moderation policy. I join the other users who have already said, "link, please?" to follow up statements of the nature of "In each case nothing I'd ever said would be considered trolling by any rational observer," so that we can all see just what the problem was. I had showdead on for most of 2010 and 2011, and I never felt, as I read dead posts, that users who don't see dead posts are missing much from the thousands of posts here on Hacker News. The way to get a reality check on this statement, of course, is to turn on showdead and see what dead posts look like day after day after day on a variety of subjects in a variety of threads.