Race and gender are about who you are and are unchangeable (transgender cases aside). Actively pursuing a homosexual sexual orientation is about what you do. Opponents of gay marriage often say that there is nothing wrong with being gay, the only problem is gay sexual activity.
To hold this position, however, you have to abandon a culturally popular belief, that a sex life is essential to human happiness.
For example, colleges like Wheaton College are often accused of discriminating against homosexuals because they have code of conduct that proscribe homosexual activity. But did you know that a Bible professor at Wheaton College, Wesley Hill, is openly gay. Ah, you say, that doesn't count. Hill is committed to a celibate lifestyle. But he is not only a gay man, he's most certainly NOT in the closet.
But if a sex life is essential to human happiness, what happens to people who can only pursue that happiness with children? What about persons with a spouse for whom intercourse is painful? What about someone married to someone whose sexual ability has been destroyed through injury?
Since I love to illustrate points with songs, this song, Ruby don't take your love to town, is about a man injured in Vietnam whose wife has decided to run around.