A legal marriage license is more than just a piece of paper and saying "I do". Tax laws, inheritance laws, insurance provisions, and pension rules are different for legally married people than for single people. In most cases these laws and rules favor married people. A Gay or Lesbian couple can be together for 35 years, but the law treats them as if they were mere roommates.
A married couple can file a joint tax return. An unmarried couple must file using single or head of household status.
A married person can obtain health insurance for his/her spouse through work. If the employer pays some or all of the cost of the spouse's health insurance, it is a tax-free benefit. If an unmarried person has domestic partner coverage for his/her partner, the benefit is treated as taxable income to the employee. If an employer has fewer than 20 employees, they are often prevented by the insurance provider from offering domestic partner health benefits to their employees.
An unmarried partner receives no Social Security benefits from his/her partner's account.
When a married person dies and leaves a 401(k) or IRA
to his/her spouse, that money can be rolled over into the surviving
spouse's IRA tax free. When an unmarried person dies and leaves a
401(k) or IRA to his/her partner, the funds become immediately taxable
to the partner.
Once same-sex marriage becomes legal reality in the state of Washington, all legally married couples would be treated the same under Washington law. Eventual repeal of the DOMA will be needed to secure equal treatment of married couples under Federal law.
If the Federal DOMA were repealed, taxpayers could expect a "fairness bonus" -- the non-partisan Congressional Budget Office estimates that marriage equality for same-sex couples will reduce the tax burden on all taxpayers by 400 to 700 million dollars annually. See the full CBO report (Adobe Reader required).
The CBO study shows some of the ways in which marriage imposes responsibilities that benefit the larger society. By preventing same-sex couples from taking on the responsibilities of marriage, their fellow citizens are denied those benefits.