I came here in 2019, and I personally think, HN is LinkedIn but with anonymous people. Most people I know professionally know my HN handle. At least for me, the idea of HN being a place where people exercise free flowing polarizing ideas is pretty foreign. Everyone here follows a particular framework, but I wouldn't call it monolithic.
I am not exactly sure, how it was 5 years ago, but I have seen some older HN users. They are busy with their family, and they have outdoorsy hobbies now. So, I think you will always see new blood in this place with different ideas and cultural values, while the older users getting more interested in carpentry or sailing their boats.
What are you expecting, a post where you say "you're not allowed to talk about controversial topics"? No, the way this works is that a controversial topic comes up, an interesting conversation ensues, you see something you don't like, and the post gets removed or flagged or you come in with a vague comment like "please do not start flame wars <insert link to HN rules>", "personal attacks are not allowed <link to rules>", etc. Do this enough times and people obviously stop having these discussions. Most of the people I used to enjoy talking with on this site either no longer post here or treat HN as a sort of linkedin, as the ancestor post described.
You are not directly responsible for all of this - there is also a less tolerant culture among commenters, resulting in massively more echo-chamber-ish voting and flagging patterns, as well as a tendency to bother people off-site. I have started using nym accounts because in recent years, people have tried to harass me or my employer over posts that wouldn't have garnered any special attention whatsoever 5-10 years ago. This cultural shift is (I think) partially due to growth, but also partially due to the culture your moderation techniques encourage (intentionally or not). The culture of rigorous open discourse over novel/controversial topics has been almost completely destroyed here, in favor of a culture of facially polite business-friendly chatter (i.e. linkedin).
I think I understand the constraints you are operating under, and this outcome is a not-unreasonable compromise given those constraints, but it is not the one I would have picked. We already have linkedin for this. HN used to serve a different (and arguably more socially useful) function, and it still could, in theory.
When you make a categorical claim like "X type of discussion is ruthlessly suppressed" on HN, I think it's reasonable to ask for links to where this ruthless suppression is showing up.
You've given an abstract answer, but what would be helpful to me as the alleged-ruthless-suppressor are specific examples. If the phenomenon is as significant as you say, links ought to be easy to come by.
And on the flipside to dang's question, do you have any links to some threads from the good old days you're describing? It'd be interesting to read through them.
I am not exactly sure, how it was 5 years ago, but I have seen some older HN users. They are busy with their family, and they have outdoorsy hobbies now. So, I think you will always see new blood in this place with different ideas and cultural values, while the older users getting more interested in carpentry or sailing their boats.