The argument is not that relationships are a waste of time, it's that heteromonogamy wastes women's time.
My point is that we live in a culture that tells women that they can't have children until they've found a man who wants to "commit" and that given that women's fertility is time limited, that that culture puts women at a disadvantage.
The thought experiment is to imagine a world where women choose when to have children whenever they choose throughout their lives, regardless of their relationship status. So maybe a young woman decides to have a child straight after college before further study. She gets pregnant by a close friend "with benefits" who is involved with their child. They never life as a couple.
Then she qualifies and works on her career for a while. By that stage she is in a steady relationship so has another two children by her then partner. She gives up work when the children are small and starts her own company. Her relationship breaks down, but as she approaches menopause she decides to give motherhood a last chance. She is single, so uses a sperm donor.
During her 30s she has also donated eggs to a gay couple who wanted to have children by a surrogate.
A woman who lived her life like this would be excoriated for having 4 children by 3 different fathers, for getting pregnant before starting her career, for being an older mother. That's not how the script is meant to play out.
I haven't said anything about individual dilemmas, or whether relationships are worthwhile.
I'm a part of that culture too. I'm a fully paid up member of team heteromonogamy - I would not have chosen to have children before being married. I don't think relationships, or careers are a waste of the time of individual women who care about them.
The point is that as a culture, the message we give to women about how they should live their lives wastes their time. It tells them to put an enormous amount of energy into maintaining relationships, even crap ones, because they are a good in and of themselves.
Look at the Relationships board when a childless, unmarried woman comes on to complain about her boyfriend being rubbish - people will tell her that "relationships are about hard work" and that you need to take the rough with the smooth. But the reality is - NO YOU DON'T. If a relationship doesn't please you, particularly when you have no commitments to someone at all, then you end it. Why stay?
The answer frequently comes down to time "invested" in the relationship. But what's the return on the investment?
The return is a hoped for future with children and security.
That's the incentive for women to stay - because they have absorbed the message that they need to wait until a man agrees before they have children. But the reality is that they don't have to wait for that permission. There are other ways.
Interesting point about an infertile spouse. I don't think it really fits into the "wasting time" argument. Although I guess a lot of time can be wasted in pursuing fertility treatment with someone rather than leaving them to find someone else.
Certainly a decision to stay is culturally determined, and probably part of the same heteromonogamy that wastes women's time in other ways. Maybe it protects the infertile at the same time that it damages the fertile?