"I'm going to get down voted for saying this" is the HN equivalent "I don't mean to be a jerk, but [says jerk things]".
Just to be a complete hypocrite: I personally don't think it's unreasonable to express a likely contrarian viewpoint and apologise in advance for that - but hey, I'm British, and some of us were brought up to be polite.
Given the wide range of opinions expressed on HN, you can reasonably assume any opinion you express will be contrary to some of them. Expressing the expectation of downvotes is not apologizing in advance. "It may not be a popular opinion, but ", or "I'm sorry, but I've never understood..." are two alternatives. I'm sure there are better ones.
It's also important to consider whether it's worth expressing what you want to say if you also feel you need to apologize for it. Over half of pieter1976's initial comment is about the downvotes, including a Paul Graham reference justifying expressing a contrary opinion. The referenced essay specifically discusses this:
When you find something you can't say, what do you do with it? My advice is, don't say it. Or at least, pick your battles.
...
The most important thing is to be able to think what you want, not to say what you want. And if you feel you have to say everything you think, it may inhibit you from thinking improper thoughts. I think it's better to follow the opposite policy. Draw a sharp line between your thoughts and your speech.
Is ignoring community guidelines worth expressing the opinion "I have never understood the raising up of Aaron Swartz to demi-god status by this community"?
Neither do I! There is a subtle but important difference between "pardon me if I'm missing something, but..." or "from the other comments on this thread it seems X is a widely-held view; I can't, however, seem to get my head around Y aspect of X" and advertising one's expectations of being down voted.
The former makes an effort to make sense of the views one disagrees with. That shows respect for the speaker. The latter dismisses it off the cuff.
If you're expressing a contrarian view, express it. If you want to apologise for it, do so politely. Better yet, incorporate why you think others will disagree into your response. Preemptively complaining, without offering any reasoning, is petulant.
They don't. The majority of people will downvote the comment because they disagree with it.
There is no way to disagree with the groupthink, without expecting to be downvoted.
I personally would love it if downvotes required an explanation. Such would be a great way to separate the "your comment was out of line for legitimate reason" type of downvote vs. the "I'm downvoting you because you're wrong and I'm not even going to say why" type of downvote.
You can learn something from the former type of downvote; the later sort of downvote is completely useless.
It comes down to, its more effective to lead a conversation than to just dispute and disagree. Its true on the internet; its true in person.
Then expect to be downvoted without explicitly posting that expectation. Nothing good will come of it.
Please resist commenting about being downvoted. It never does any good, and it makes boring reading.
Please don't bait other users by inviting them to downvote you or proclaim that you expect to get downvoted.
https://news.ycombinator.com/newsguidelines.html
You may not agree with it (which is fine), but it's largely accepted by the community.
The trick, William Potter, is not minding that it hurts.