Government should not be in the marriage business. Although it absorbed much older secular marriage codes, marriage is a religious concept. It legitimizes sex between a man and a woman, essential for procreation which some churches see as the primary or even only legitimate purpose of sex. Churches should be free to marry, or not marry, whomever they see fit, and indeed this is the case. Government should have no interest in whether people are married or not.
Family law addresses two fundamental government interests: supporting the commitment of parents dedicated to the growth, education and socialization of their children, and supporting the ability of people to provide for one another in committed relationships, recognizing the full range of healthy, non-exploitative romantic partnerships
Government does have an interest in stable families, in promoting and supporting the natural inclination of couples to be committed to one another and to their children. If the commitment is in the form of marriage, this of course supports the secular objective of stable families, but it is not a requirement for that. Civil marriages performed by judges or other officials recognize the public interest in stable commitments. These civil marriages do not embody any religious commitment and are essentially civil unions. Similarly, many states recognize Common Law Marriages, considering couples who have demonstrated commitment and devotion to one another as married and granting them many of the rights and privileges afforded married couples. But of course these are not marriages at all. In most cases there has been no specific public commitment to one another, and often not even a private exchange of commitments. This concept of Common Law Marriage embodies the need for civil recognition of couples who are dedicated to one another.
A number of states recognize a status of civil union. This gives couples an option of making a public commitment to one another without the necessity of religious or pseudo-religious ceremonies. Civil unions are indeed what governments have a legitimate interest in. It is not incongruous to recognize religious marriages as constituting civil unions, but this is not necessary. Indeed, if some church wishes to perform marriages that unite couples spiritually without committing them to intimate relations or raising families, this should not be a matter of civil interest.
Children raised by both a father and a mother generally do better and it may be that marriage does support stronger commitments to child rearing. A firmly shared religious bond can add stability to a relationship, though current high divorce rates call even this into question. Even more so, the high rate of children born out of marriage shows an increasing public rejection of marriage. Children being raised by non-traditional couples may indeed fare more poorly in life, but limiting important benefits (such as health care or family leave) only makes the situation worse. It certainly does not support the civic interest in promoting child development. Other benefits (such as hospital visitation, heath decisions and survivor benefits) which are available to those in marriages should be available to any couple that professes a dedication on each other. There does not need to be any automatic link between religious marriages and secular civil unions.
Governments should eliminate marriage as a term in civil law.