Meanwhile personal attacks and hyperbole regarding Elon Musk and Trump have become very common on HN.
Speaking from personal experience only: I have mostly not observed "polite, well-worded posts disagreeing with the mainstream" get downvoted to oblivion, unless some other factor also applies, such as that they're also things that seem likely to lead to a rehashed old-as-the-hills disagreement with no new information that will not on balance change any minds.
If you post (by way of example only, please observe the use-mention distinction here) a polite version of "ads are good and adblockers are stealing", and get a massive pile of downvotes, I think that's a reasonable signal that the community isn't interested in seeing iteration 47,902 of that argument, and has no expectation that anything new will come out of that argument. If you have something new to say on that topic that is likely to lead into new and interesting arguments, at this point you would need to signpost that heavily, prefacing it with some equivalent of "Please note that I'm aware this is an age-old argument, but I think I have a new point to make that is worth considering", and then actually make a new point, at which point I think you're less likely to get downvoted to oblivion.
Personally, I don't downvote "mere" disagreement. I downvote (among other things) what seems to me to be uninteresting or thoughtless or insufficiently diligent disagreement, or factually incorrect information, or anything that seems like a discussion that spawned from it will not be interesting.
Now, that said, another factor here is that some people posting on political topics in particular believe they're making "polite well-worded posts disagreeing with the mainstream", and others do not share that belief and flag it to oblivion. For example, posts expressing bigotry mostly get flagged, no matter how surface-level "polite" they are.
Sure, I imagine the grandparent poster means arguing something like "limiting access for extensons is good because they're often used to steal financial assets". Old extensions are sold, or cracked and updated to inclue malware.
Why is this required, in order not for the comment to be downvoted to oblivion? You may be confusing bias with nuance.
(It's still regularly abused on stories as a downvote, perhaps in part because stories don't have downvotes. HN sometimes "rescues" stories that get over-flagged, but it's still a problem.)
Personally, I’d prefer no up-/downvoting and flagging at all (or flagging only to alert moderators), and purely chronological threading. But I also think that active moderation and crowd-sourced ranking mechanics are two different things.
I think that's a very different kind of forum, and it needs different tools to be usable, and it more quickly fails into unusability.
For example, I think it's useful that on balance the top few comments and their discussion are likely to be interesting, and the last few comments are unlikely to be interesting.
That's not a moderation issue. You can post that opinion, and people will disagree with it, post responses to it, and downvote it. It will not be flagged out of existence, unless it's also violating site policy in other ways.