> I think that "high investment" is an important note. Even in dual parenting situations, the temptation is to want parenting to be low-investment. (I'm a parent; I definitely struggled with that.)

Missing the point. I'll quote my other comment:

"Even if we pretend both parents provide the exact same types of resources (which they don't: both are important for different reasons), then mathematically you're getting half the resources to raise a better kid."

We can make this argument apply for money and time, both of which sound like pretty important things to put into a kid. Both of which are practically gauranteed to be less when there is a single parent.

> But from my outside perspective, I would think that it might be preferable to abuse, though maybe not preferable to almost anything else.

Nobody's arguing that two parents which are abusive would be preferable to one who is not. I believe this is called the Red Herring fallacy. My point is that it is irresponsible to promote alternative family arrangements which are strongly correlated with worse outcomes for children, without at least considering these correlations first.