Yes, we need a place where we can discuss things line this without parents butting in and saying their lives would have been empty and pointless if they hadn’t had children.
Agreed; I hope the existence of a specific board, with guidelines about being respectful to those the board is set up for (like some other boards have), would clearly telegraph that these are legitimate parenting-related discussions to be having on MN, and that within that particular space, comments of the type you mention aren't helpful. (Well, they're unhelpful in some other contexts, too, but as you say, a place where those comments are more explicitly unwelcome might be useful.)
However, I do think there's some value in recognising that one of the benefits of having such a board specifically on a site like MN is that, sometimes, there may be perspectives a parent may be in a better place to put forward, or there could be parents with relevant insights on particular topics or points raised.
Having a board like that within a large, busy general parenting forum could facilitate that sharing of views and info, within a framework explicitly focused on those who don't have children, while also helping to avoid the polarisation between viewpoints that can come when people are completely separated off (which I think can sometimes contribute towards people adopting some of the more extreme language or views mentioned upthread).
I also wonder if there's some value that comes from posters on any "MNers without children" board being aware that parents, possible future parents, and non-parents alike may read their posts — and whether the existence of the board might make posters elsewhere on the site who are parents also be more conscious that their posts may be read by parents, possible future parents, and non-parents alike.
Meanwhile, it could also give those who have had (or may/may not in future have) children more insight into aspects of the lives and concerns of those without children which are different because they aren't parents (which they may not always discuss IRL with those who are/may become parents), showing them a group of ordinary people who don't have children and aren't anti-natalists or child-haters, just people living their lives and talking about those aspects of parenting/its place in society that affect them, due to their nonparticipation.
Hopefully, given the existing culture and demographics of MN, and some thought given to both the message at the top of the board and the moderation style used, it would remain a thoughtful, civil place to discuss how non-parent status operates within the lives of, mostly, adult women, generally living in the UK. Not that others wouldn't be welcome, but AFAIK that's who makes up the bulk of posters. That demographic doesn't really predominate elsewhere online, and many existing places on the internet where people discuss life without children are coming from quite a different perspective.
If well-moderated, it could help humanise and normalise those without children and their lifestyles, and reflect some of the paths someone's life can take — some of which, on MN, seem to come to a bit of a dead end. If you come to MN before children, you might look at the different parts of the site about relationships, fertility, different ages of children, having adult children, but there's not much about what comes next if children don't happen.
People could argue that it's a parenting site so if you don't become a parent you go somewhere else (or say that there are other boards on MN to chat on, which is true) — I talked about my counterargument to that in my previous post. But this missing "path", of what happens when becoming a parent doesn't happen, feels a bit to me like it reflects our society, and not in a good way — the way that not becoming a parent can feel like unmapped territory, a journey our society didn't prepare us for, where we become invisible and un-catered for.
Just seeing that such a board exists on a parenting site, that that "parenting journey" has also been considered, could be helpful for those thinking about their future WRT parenting.