I think the thing that always strikes me as nonsensical about this sort of thing is that family is always compared to the lofty mum/dad/2.4 DC 'happy' family ideal.
The trouble is, many of these 'ideal' nuclear families are hiding their own dysfunctions - DV and infidelity to name just two huge ones that are rife and yet don't always result in relationship breakdown.
IMO, a happy, stable family is one where the members all interact with each other in a healthy way, and where everyone is encouraged to pursue their own individual happiness but also to pull together for the greater good of the family overall. That can happen despite divorce, death, moving house, new siblings (by a different father) and all sort of numerous other 'traumas'.
Whereas a mother who has more children with a serial abuser/adulterer/irresponsible father may look to the outside world as though she's more stable, but she'll certainly be putting her children at more risk of emotional harm than the mother who left a bad relationship (so modelling self-reliance and good boundaries) and then went on to form a new, healthy relationship and then had another child.
That said, a mother who is on her third or fourth abusive/unfaithful partner should certainly be questioning whether her judgement needs some working on, although it's also worth asking what it is about society that places the responsibility for this on the mother, rather than the father who abuses/cheats/fails to take responsibility.