That's a real problem. Well, there are two problems actually.
One of the frequent reasons people enter into the comment box after unsubscribing is "this is way too advanced for me". So something like a Newbies Corner section would be a good idea.
I'm just not sure how to make it work without creating a big mess of redundancy between Main and this Newbie section.
If a topic is "too advanced" (by whatever arbitrary standard), then do I move it from the Newbie section to Main?
Or if someone posts a simple question in Main, do I move it to the Newbie section?
And if I don't move topics around, then we'll end up with two sections that do the same thing, because both Main and Newbie sections will over time contain both simple and advanced discussions.
Another option would be to create "Main (safe space)" section. But I'm not a fan of safe spaces in general.
Besides, it would look ridiculous. "Main Photography Discussion" and "Main Photography Discussion (safe space)" on the home page of the forum.
Still, I know of at least one forum I used to frequent around 2001-2002 (not related to photography) that had a Newbie section. Its purpose there was solely to get new users posting, so that they get over their fear of posting and get involved, and then cross over to the other sections of the forum.
It would be nice to have something like that, but as I said, I'm not sure how to make it work with Main.
The second problem is people who are rude to new users. This isn't always related to the skill level. And yes, I agree that it's doesn't present a good first impression of the forum.
But I have a fix for that. If you see someone regularly being rude to new users (especially in the Main section), then please use Report Issue link, select "other", and enter comment "rude to new users", to let me know what the report is about.
The new forum software has an option to block replies in topics of new users. So if someone is rude and condescending towards people who just joined UHH, then I can limit their account. They would still be able to post as before in topics of established users, but they wouldn't be able to post in topics that are created by newly registered users.
I forgot that I implemented such functionality while keeping this exact scenario in mind. Reading this topic reminded me of that.
Of course, that won't solve the first problem of people who are shy about posting or think that this forum is only for advanced photography discussions. But taking care of rudeness towards new users might be the first step.