Don't let anyone tell you that federal policy should be neutral about marriage, children and the family. There is no such thing as a neutral tax or a neutral deduction or a neutral credit. Every part of your income tax return that you will file in April is a manifestation of some social policy. The whole concept of those who have more income paying higher rates of income tax than those with less income is a decision of social policy. It's social policy that we can deduct gifts to religious and charitable organizations, and for retirement savings. It's social policy to promote home ownership by being able to deduct mortgage payments.
Traditional marriage has been specifically favored in the federal income tax law since Congress created the joint income tax return in 1948. This enabled married couples, where the husband is the principal breadwinner, to file their income tax return as two people, which they certainly are.
Unfortunately, fiscal-social policy in the income tax code and in government spending has steadily devalued marriage and subsidized non-marriage. Unmarried persons with children are permitted to file as "head of household" and are eligible for the same per-child credits and deductions as married couples. If the single mom cheats and has a live-in boyfriend who files his own tax return, she ends up with more favorable treatment in the income tax system than a married couple raising their own children. If we truly believe in traditional marriage, we should not allow it to be discriminated against in the income tax code.