This is a little unclear. I am not sure if your teacher means you need to see what policy resulted in allowing same sex marriage in the United States or if your teacher means you are expected to argue for or against a particular policy or position. Either way, while a statute might reflect a governmental policy, a statute is not a policy. The policy that allowed the Supreme Court to rule that same sex marriage must be allowed is the policy that all people must have equal rights under the law, a policy rooted in our Constitution. If some people can marry and others cannot, the law is being applied in a discriminatory way to a group of people on the basis of an immutable characteristic, much as we might not allow black people to marry or refuse to allow all blue-eyed people to wed. The people who were not permitted to wed had serious disadvantages, for example, in taxation, in social security benefits, and in parental rights. Another policy at issue in this area is that of the government not establishing a religion under the First Amendment. The government can make no law that imposes a burden on a group of people just because some people's religions find same sex marriage unacceptable. A governmental policy rooted in religious belief, in a country in which people are free to practice or not practice any religion, is a policy that is deeply antithetical to American values. Thus, the separation of church and state and the equal treatment of all under the law are two policies that have led us to this juncture, the freedom of all to marry whom they choose, with all the advantages (and disadvantages) that accrue.