Mike McManus, the moving force behind community marriage covenants, has a fine stump speech for anyone running for office. His argument: "divorce and unwed births are two of the engines driving up the cost of government."
In addition to all the direct costs, there are the many indirect costs that come from worse health, less education, spotty employment, and increased crime rates that we can reliably predict from marriage breakdown and single parenthood.
McManus, who is a pretty conservative guy, has a quite moderate approach to gradually diminishing the welfare benefits of cohabiting poor parents who marry. This seems like a practical and centrist approach to me.