I'd say it's more citizen-level apoptosis. These women are the ones exiting the gene pool, not the whole civilization.
But also 4B is an outsized meme especially in the west. It's like furries. We all know about them, but they are not typical people who you can draw conclusions about the civilization from.
The women aren't the ones detecting they have something wrong with them. They are detecting there is something wrong with the next level up, and shutting down that whole thing. Like an apoptosis gene triggered by excessive misfolded proteins.
But in reality they aren't "shutting down that whole thing", they are shutting down their personal lineage and not much else. The women might not be conscious of something wrong with themselves, but if they were cells in a body, their behavior would not indicate the body is sick, only that they are.
But also 4B is an outsized meme especially in the west. It's like furries. We all know about them, but they are not typical people who you can draw conclusions about the civilization from.