May I ask why? As someone who considers that the one change/improvement I'd like to see on HN I'm curious what there is to be leery of that I may not have considered.
Because this isn't like reddit where the most upvoted comments are elevated in otherwise collapsed threads. I've only read some of the most insightful and interesting comments and discussions on HN buried most of the way down the page because they were available for me to see despite their lack of being voted on. On HN, popularity isn't valuable, the ideas are, and non-precollapsed threads support that.
Sometimes the good stuff isn't even on the first page. For example, see [0] (scroll down to the follow up) and the HN discussion [1] referenced there. Also, collapsible threads doesn't have to mean pre-collapsed threads.
To me it seems like collapsible threads would help, not harm, in this case because more people would have collapsed the OT first thread and participated in the discussion about the actual topic. I realize there are two assumptions built in to the above that may not always be true: 1) OT threads are bad or less desirable and 2) more people in a discussion is better.
I'd argue that the main point of collapsible (not pre-collapsed) threads is to support what you're saying. When a comment spawns several pages of discussion on a topic you're not interested it, collapsing it would let you go directly to the next comment you are interested in, surely?
Right now, for me at least I often just scroll down to the next top-level comment because it's a bother to find the end of a comment tree that started several indentations in.
I use Reddit Enhancement Suite to collapse all child comments by default, then open interesting top-level comments in a new tab to read the full discussion. I probably miss a lot of good discussion on HN because it doesn't support something similar.
That concern could easily be remedied by having thread collapsing be an optional setting in your account. I personally think having every thread collapse after a certain depth would make it much easier to tell which threads are probably worth looking deeper into.
May I ask why? As someone who considers that the one change/improvement I'd like to see on HN I'm curious what there is to be leery of that I may not have considered.