> to me the difference is plain to see.

Agreed. HN isn't 100/0 signal/noise or even 100/0 politeness/rudeness, but I get the feeling most people discuss things with a relatively open mind here, and it's not uncommon for people to either be corrected by others and accepting it, or correcting themselves if they've found something out after submitting their comment. Just seeing that happening makes me hopeful overall.

It's a huge contrast from basically any mainstream social media, where the only time you'd see something like that is when you're talking with literal friends.

> HN is low on ad hominem attacks, excessive straw man arguments, there is a good amount of polite disagreement, and people are often amenable to being wrong.

That's is due to active moderation, but it's orthogonal to being in a bubble. There are also some very similarly moderated, polite communities on other platforms, even Facebook, but they're still bubbles. People on HN are already self-selecting to an extent, and if you stray to far from the core audience, you'll be downvoted to dead.

That's how the forum is designed to work, but it is definitionally a bubble.

> If this seems no different from the big commercial platforms to you, I frankly don’t know what to say, to me the difference is plain to see.

It is no different to the other well-moderated communities on the other commercial platforms. The only difference is that you like this bubble more than the others.

> You don’t need to be 18 to have a bank account, even in the UK (which just introduced age verification laws).

Yeah, I had one of those myself when I was under 18 too, I think it was called Maestro or something similar. However, it didn't work like a normal credit card (which I think only 18+ can have), platforms were clearly able to reject it, as most things I wanted to buy online didn't work at the time with it (this was early 2000s though), only with my mom's debit card.

Probably the same is true for those cards you linked, they're special "youth" cards that platforms could in theory block? Then requiring credit card "donation" of $N would still basically act as a age verification. I think debit cards might in general be available to people under 18, so filtering to only allow credit cards sounds like a start at least.

Newgrounds literally employed the same strategy for automatically validating a bunch of users, from https://www.newgrounds.com/bbs/topic/1548205:

> 2. If your account ever bought Supporter status with a credit card and we can confirm that with the payment processor, we will assume you are over 18 because you need to be 18 in the UK to have a credit card.

Basically, filter by the card type, assume credit = 18+, any other might be under 18.

> One mitigation around that could be the gifting of accounts

Yeah, referrals ala Lobste.rs. I feel like they get lots of stuff right, from transparent moderation to trying to keep it small but high-quality. The judge is still out on if they got it right or not :)