As I argued in “What I Think Principled Centrism Means,” a centrist wants to promote what is best for society, tolerate what is good enough, and prevent what is harmful. This means that to define a centrist policy about anything, we need a category of social practice between the preferred and the prohibited. The natural thing to call this category is “tolerated.”
For example, historically and cross-culturally, marriage is the preferred institution in which to raise children, and incestuous unions are a prohibited way. What centrists need to be able to say is that marriage is preferred for raising children, and some other ways – my nominees would be single parenthood and same-sex unions -- are tolerated, acceptable, good enough. This is true of any social policy. The best way is still better, and social policy should provide incentives to promote the best way. But those who fall in the middle category, the good enough way, should not be penalized beyond the natural inefficiencies of doing something in a less than optimal way.
For liberal egalitarians having any kind of second class status is unacceptable.
For conservative perfectionists permitting any but the preferred way is to connive at social breakdown.
The primary political and philosophical problem of centrism is legitimizing the distinctions among the good, the bad, and the good enough.