I had a fleeting worry this morning that we might not have much to discuss. I was wrong.
First, your point on Deutsch: that less affluent couples who use tag-team child care aren't able to spend time together and thus might experience strains in their marriages. To my eye, however, it is not the less affluent couples whose marriages seem more strained. It's the academic couples. As you note, they have more flexible work schedules and huge chunks of salaried time out of the office. They also use far more day care than the less affluent couples. (A lot of the professionals seem to see child-rearing as blue-collar work, and unpaid blue-collar work at that, so they resent it.) So the chief source of marital stress for these couples is not time spent away from each other on care for the kids but conflict over who gets to spend more time pursuing professional work. Much of the time they spend away from the kids they also spend away from each other – not smooching in front of the fire. I feel their pain. I live in the same ZIP Code as many of the academic couples in this study, and it is hard to find two good teaching jobs in these parts. So I suspect they are particularly panicky about their careers. Still, though professional couples do not rely on tag-team child care, they don't devote significantly more time to each other than the less affluent couples. If too little time together is a source of strain, it strains the professional couples too.
As for the less affluent, most of those with tag-team arrangements say they have chosen them over day-care centers--partly to avoid the costs of day care but mainly to take care of their kids themselves rather than turn them over to a "stranger." This is an affirmation of what they regard as important in life. When I did a study of child care preferences among middle-income working parents in the 1980s, I found the same thing--much to my then-surprise. In fact, I found that couples turned down job promotions that might disrupt tag-team arrangements. So I suspect that there is less strain on the marriage as a result of tag-team arrangements than you would think.
(Note: The tag-team couples have median family incomes of $43,000. This puts them in the middle of the family income distribution. Families farther down the economic scale face all kinds of strains, including many not of their own choosing.)
Nevertheless, you do identify a dilemma: What a child-primary couple might do for the sake of the kids might not be that good for the marriage. And if such pressures in the marriage lead to severe marital discord or divorce, that's obviously bad for the kids. So what's a couple to do? All I can do is invoke the Boy Scout rule: Be prepared. Since you're about to become a father, here's something to ponder. Marital quality declines when kids arrive and it goes up again when kids leave. Think of marriage as divided into the erotic years, the pediatric years, and the geriatric years. The pediatric years can be tough. And, yes, kids often strain and always change marriages. This is a clue to why so many marriages break up during the first five or six years. A lot of couples have children in the first few years of marriage, particularly since people marry later now and often have kids right away in a race to beat the biological clock. Better for couples to learn this in Lamaze class rather than in court-ordered divorce education classes. Maybe if couples knew beforehand that their relationships would change when children arrive, they might not confuse being sleep-deprived with falling out of love.
Now let me go back to Deutsch and give her some credit: Her book provides useful evidence on what seems to work best in sharing child care and paid work, though she doesn't highlight it. I jotted down four success factors: commitment to fairness in sharing family responsibilities; dedication to the marriage; a mutual focus on children as the top priority; and a common mental commitment to the work of the household. Mental commitment to the work of the household means you carry a list in your head of what has to be done for the kids, meals, laundry, toilet paper replacement. How about it, guys?
Re: The Mason book. You're right. I don't like the idea of creating the new legal status of "de facto" parent, but not chiefly for the reason you suspect. And I didn't leave myself room today to write about "why pro-child liberalism doesn't thrive." I'll try to get to it tomorrow.