Conceptually, here's what I'm saying. In a divorce, three things are being dealt with:
1. Status adjudication of the marriage.
2. Property division.
3. Parent-child relationship.
It's settled law that #s 1 & 2 are functions of the marriage contract (or the "marital estate").
It's settled law that #3 is different than #s 1 & 2. Each parent has a separate and complete set of parent-child relationship rights that's independent of the existence of marriage, or the existence of the other person.
Arguendo, let's agree that the state may make a variety of rational choices about how to deal correctly with #s 1 & 2. It doesn't possess the same latitude about #3. It's self-evident that in dealing with the parent-child relationship we're dealing with (as we say here in Tejas ) "a whole 'nother country" than those other subjects.
In application, we really should be looking at both Ejusdem Generis and In Pari Materia, viz.:
If on Day X the state exercises power to interfere in the parent-child relationship of Father A and Mother B, either as a couple or separately, the state may do so only upon a showing of probable cause that one or both parents is abusing or neglecting their child(ren).
If on Day X+1 the state exercises power to interfere in the parent-child relationship of Father A and Mother B, either as a couple or separately, the state may do with impugnity.
Question: What happened in the intervening 24 hours?
Answer: Father A or Mother B filed a No Fault petition for divorce that failed to allege any sanctionable parental behavior on the part of the other person.
This is impermissible in a society that's based on Liberty.
So much for law.
As a matter of history what I think happened is that the application of British common law parens patriae power made sense in a divorce context that was always, by definition, based on fault (usually adultery or abandonment). When the states went to No Fault, something very important happened. Arguendo, No Fault perhaps made sense for #s 1 & 2. But parens patriae applied to #3 in a No Fault context made no sense. What I think happened is that the issue wasn't raised because we were in a strange historical interlude of confusion about distinct familial roles for moms vs. dads.