As of 12 November 2013, 16 states allow same-sex marriage. 16 out of 50 states is a horrific amount.
The Constitution allows for all Americans to have the freedom of religion. Therefore, anybody can believe (or not believe) in any religion.
In the United States, marriage is secular and is not bound by religious beliefs. It is a basic civil right for U.S. citizens to get married.
Therefore, it is extremely discriminatory for same-sex couples to be denied marriage in states that do not allow this marriage simply because of religious morals.