It's a hard question to answer. It's healthy in that it encourages discussion due to skeptics of all kinds. However, it can get very pedantic at times, where some people nitpick not over the post itself but some non-pertinent detail about the post, such as the title, website loading speed, trackers, and so on; the content metadata, as it were, rather than the content itself. This is quite annoying to read through. If I were to make a new forum, I'd want something like the following stipulations for posters:

- Steel-man all arguments: consider the best possible interpretation of the argument, and if you need to, consider playing the devil's advocate not only for the post you are replying to, but also your own post. I've written a lot of philosophy papers and they strongly advocate this point, that you must consider each and every single counter objection. I know that HN rules include consideration of the best possible interpretation, but it may not be enforced strictly enough.

- Do not comment if you cannot do the above. This includes short one sentence comments that should be permitted if they truly and exemplarily contribute to the conversation, such as a necessary piece of information. Too often I see pithy quotes or humor, which, while interesting, are not very suitable to argumentation in the formal sense.

- Focus on the main content, not metadata. As above, many posters comment on something that is not part of the content but its metadata. This goes hand in hand with the "best possible interpretation" clause. If you so feel the need to nitpick over the title, do so only after addressing the content at hand.

How does one achieve this? People run on incentives, so the design of the forum must incentivize people to act in this way. On one end you have Twitter, which incentivizes short, flame-baiting "hot takes" over long-form discussion. This is inherently and entirely due to the _design_ of the site alone, where the 140 (now 280) character limit creates these incentives. On the other hand, you have academic paper communities, which incentivize understanding long-form content lest a reader misunderstands a paper, creates an opposing paper, publishes it, and is socially ridiculed for not having noticed the misunderstanding sooner. In other words, the design of the forum incentivizes the reader to digest content fully. The hypothetical forum would stand somewhere in the middle.

Now, to achieve this in practice, versus theory, there are certain designs you can have to do so:

- Strict moderation. This is similar to the moderation levels of /r/AskScience or /r/AskHistorians on Reddit where low-effort comments and even branches are removed. This is the easiest to implement technologically but also the hardest sociologically, due to needing manpower and choosing acceptable moderators.

- No downvoting, and no showing numbers of votes. HN does this well to some extent, but you still see branches downvoted for differing opinions. Perhaps one can only downvote or report posts with a rational reason, basically held to the same standards as if they were to reply to it.

- Randomizing content to a certain degree. HN and Reddit have algorithms to do this so that the top-most content is not always shown.

- Sorting and filtering any and all posts based on content and votes. This is more of a convenience feature but I wish more sites could let you sort and filter by certain tags or number of votes, and by date, like reddit and HN with the Algolia search.

That's what I've thought of for now, I know it doesn't exactly answer your question but these were a few things that annoy me about most fora.