>> HN is unabashedly homogeneous.
I think you've summed the nature of HN pretty well. I wish I knew that before I joined (recently), but unfortunately I had to learn it the hard way.
>> The set of opinions that will not get you downvoted into oblivion / pushed out of the community is so narrow...
That is exactly the conclusion which I arrived at after about three weeks of active participation. At that point I lost any interest in continuing trying to become a part of the community.
In my opinion, the HN community is not very healthy and has become incestuous in its nature. People basically choose to exchange with the like-minded only, share the same opinions, upvote the things that match their view of the world and downvote deviant opinions.
This all is aggravated by the fact that the HN user base is mostly North American and visitors from other world regions are somewhat of a minority in here (my observation). That's why a lot of ideas and opinions that I see around here are just "alien" to me, although I've never had a problem finding a common language with Europeans, for instance.
In its current form, I can often look at any new question that comes in here, and if I have seen its equivalent on HN before, I already know what will be the most upvoted comment and what kinds of downvoted comments I will find at the bottom of the page. The mechanics of HN is such that it works as a giant "echo chamber" and users are "taught" which kind of opinions they're supposed to like, support and help to spread and what will happen to them if they defy the state (downvoting sanctions).
I'm sure many like this way of things, but the way I view it you can't have healthy offsprings (which are ideas and opinions) if your community embraces incestuous relationships as its core defining value. Without diversity, there is no evolution.
On a related note, I used to be one of the early users of StackOverflow/StackExchange sites. In its first couple of years they had a liberal content policy and this invited a healthy, diverse and vibrant community that produced many profound and wise ideas. When they went down the deletionism route and started discouraging deviant opinions, the most interesting people started to quit and in about a year or two the sites degraded to such an extent that made it pointless to return in the search of quality content.
HN is not there yet, as I still see some high quality answers now and then. Usually they're neither upvoted not downvoted, they just stick somewhere in the middle-bottom area and I have to dig for them. Sadly this requires much time which I'd rather spend on more important things.
I also very much dislike that anti Russia/China/Turkey/Islam rhetoric that comes every now and then. It's not that bad as on Reddit where you can just say some not very intelligent bad thing about those countries and get yourself a few hundred upvotes and a dozen gifted "reddit golds". That's just the new bottom that Reddit recently hit. I sadly see HN moving in the same direction.
>> assuming you like a decent proportion of highly upvoted submissions and comments, you'll almost assuredly like all of them.
>> There are plenty of people who don't. They are just not on HN (anymore).
Apparently I'm with that group as I no longer have any wish to hang around HN. At that point I'd be ashamed to admit I've tried to be a HN member, as it would be an embarrassment to admit to having an active SO/SE account these days. To me, that was a mistake in judgement. I'd like to delete my account and make the divorce official, but apparently HN does not allow that and does not buy into the "Right to be forgotten" idea. I have no doubt that most of the HN users share that same official opinion being the "example citizens" that they are.