 Some arguments against same-sex marriage invoke a precautionary principle urging that changes which might affect child welfare be made with extreme caution. But in light of the data available, Murphy argues that the precautionary principle has been met with regard to harm to children. On his view, parenting is a basic civil right, the restriction of which requires the threat of a certain amount of harm. But social science literature shows that children are neither typically nor seriously harmed by same-sex parenting (see Manning et al., 2014). Even if two biological parents statistically provide the optimal parenting situation, optimality is too high a standard for permitting parenting. This can be seen if an optimality condition is imagined for other factors, such as education or wealth (Murphy 2011).