Recent work by Benjamin et al (2013, 2014) confirms that people do not exactly maximise their wellbeing when making life decisions, but they often come very close. If so, those whose wellbeing will be improved by having children will have children, and those whose wellbeing would be worsened by having children will not. But the two groups have different tastes – most obviously in their preference for children – so we have no a priori basis for expecting one group to be better off than the other once they have made their choices. Would be parents who cannot have children are certainly likely to be dissatisfied relative to those who do, and people who do not want a child would no doubt be dissatisfied if they accidently acquired one. But non-parents are not failed parents, nor are parents failed non-parents.
And that is about all that we can say.
The concluding remarks of a monograph by economists Angus Deaton and Arthur Stone, peforming an analysis of claims that parents or non-parents are happier or less happy than they would be otherwise.