The battle over the right of Americans to participate in same sex marriage has been hard fought in both the Supreme Court and the court of public opinion. After emerging as a new civil issue in the 1970s many have weighed in on both sides and some have actually won the battle in their home states. Those states are California, Connecticut, Delaware, Iowa, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Rhode Island, Vermont, and Washington. The others have been battling to keep the their current laws in place amid opposition from civil rights activists across the country. In the 70s the fight for gay equality began for Americans and in 1973 they had their first success when the American Psychiatric Association removed homosexuality from its list of mental disorders. That was one step in the right direction but it was the only one for a while until in 1993 the United States military agreed to let homosexuals serve under the new "Don't Ask, Don't Tell"" regulations. This stated that they can join but only if they do not disclose their sexual orientation to anyone. I guess this was a step in the right direction but it was only the beginning. In 2000, Vermont became the first state to allow same sex civil unions. Also a good step in the right direction but it still comes up short of granting them full legal marriages and the benefits that come with it. Then in 2003 in Texas the law that was long upstanding of a ban on sodomy was found to be unconstitutional by the U.S. Supreme Court. Soon after in May of 2004 the state of Massachusetts became the first state to fully legalize same sex marriage. From here the battle continued state-to-state, winning in some and getting shot down in others.
The main argument here is if under the constitution all people are allowed to marry or only men and women. One argument is that whether it is legal or not doesn't matter as long as the people in it believe it.