"...As we argue in our book "What is Marriage? Man and Woman: A Defense," marriage is a uniquely comprehensive union. It involves a union of hearts and minds; but also—and distinctively—a bodily union made possible by sexual-reproductive complementarity. Hence marriage is inherently extended and enriched by procreation and family life and objectively calls for similarly all-encompassing commitment, permanent and exclusive.
In short, marriage unites a man and woman holistically—emotionally and bodily, in acts of conjugal love and in the children such love brings forth—for the whole of life.
... weakening marital norms will hurt children and spouses, especially the poorest. Rewriting the parenting ideal will also undermine in our mores and practice the special value of biological mothers and fathers. By marking support for the conjugal view as bigotry, it will curb freedoms of religion and conscience. Redefinition will do all this in the name of a basic error about what marriage is.
Some bonds remain unrecognized, and some people unmarried, under any marriage policy. If simply sharing a home creates certain needs, we can and should meet them outside civil marriage.
Moreover, if we reject the revisionist's bare equation of marriage with companionship—and the equation of marriage licenses with all-purpose personal approval—we'll see that conjugal marriage laws deprive no one of companionship or its joys, and mark no one as less worthy of fulfillment. (Indeed, using marriage law to express social inclusion might further marginalize whoever remains single.)