While gay marriage is often politicized, it is best viewed as a simple union between two people. Love is love. If two men or women want to share their lives together, then they should have the right to have the union recognized legally. A gay couple deals with the same issues as a straight couple.
People have the right to choose their partner in life. Although some religious institutions strongly object to gay marriage based on their beliefs, marriage is a legal institution in the United States. The United States Constitution calls for the separation of church and state. It is, therefore, unconstitutional to deny gay people the legal right to marry.
Legalization of gay marriage is a good idea because at the end of the day, love is love. It doesn't matter if it's between a man and woman, man and man or woman and woman. Being gay or straight does not define the morals of the person, and there are plenty of straight couples who do awful things but are allowed to marry. Why should it be different for gay people? Gay people are people too, and have the same rights as straight people.
Legalizing gay marriage is one more step towards society saying that everything is acceptable as long as it doesn't hurt anyone else. This is not true, because there are certain standards set by natural and moral law which remain true regardless of what people choose to do. Many tendencies, including homosexual ones, are inherent, but the satisfying of these urges does not make them right, and they should not be promoted.