I wholeheartedly disagree. Much of the content on HN is long form journalism, some is content that is so specifically specialized in a field, that only those with thesis in that field will understand. Part of the brilliance of conversation on the web is interactions between disparate fields. On may articles, if I have to read all the way through a theoretical physics post and understand it without a synopsis, I wouldn't be able to add any value to the conversation, and the thread becomes an echo chamber. The initialism tl;dr does matter, because it's a clean and easy way to identify the content that someone looking for a synopsis will look for.

I understand the goal. HN doesn't want to become reddit, and values engaged discussion. But tl;dr isn't reddit, and it isn't going away. Language is ever evolving, and the way we talk today would have sent my granddad into a tizzy. Part of being a platform, and HN is a platform for ideas and conversations, is that the people will decide how to manage that relationship. Moderation can only trim the edges, and remove the bad actors, but the tonne and tools will not be set by moderation, but rather cultivation by the users.