 It is widely accepted that the state should protect children. If two-parent families benefit children, incentives to marry may be justified as promoting two-parent families and hence children’s welfare. One benefit of two-parent families is economic: there is a correlation between single motherhood and poverty. Another benefit is emotional: children appear to benefit from having two parents (Galston 1991, 283–288). (Moreover, some argue that gender complementarity in parenting benefits children; but empirical evidence does not seem to support this [Lee 2008, Nussbaum 1999, 205, Manning et al., 2014].)