I'll ask this in response: why does society need to exist at all?

Obviously ideas like yours are ingrained into us at a biological level and it logically makes sense if we want to survive as a species... but there is no inherent reason other than "just because" right?

Well yeah, because of our ingrained sense of morality & self-preservation. But we're talking about the policies of society so it's kind of pointless discussing them if you don't accept that society should exist in the first place.

Also... it's not society, it's the human species.

That's indeed a philosophical question. Should we even exist at all?

It's a strange thing of nature and evolution that it creates a species that can plan and execute its own intentional suicide.

It's fairly irrelevant to the discussion. All societies that choose not to exist also choose for all their policies about (not) reinforcing children to not exist.

“No children” and “single” isn’t the same, as evidenced by DINKs. That set aside, you’re just confirming that singles are (or should be) penalized.

Yes, that's just a necessity for the persistence of a society. Otherwise there's no point in even organizing as one. I'm not making a value judgment by the way, just an objective statement. I was also once part of a "DINK" and someone who thought would not have children, I have no qualms with that, but there's just no point in prioritizing that segment.