The argument I've most often seen for why sexual orientation is analogous to race is because both are not "choices": just as we cannot choose our race, so likewise we cannot choose our sexual orientation.
1. On the face of it, this conflicts with the work of LGBT scholars like Lisa Diamond. For example, see her book Sexual Fluidity: Understanding Women's Love and Desire.
Along the same lines, see Edward Stein's The Mismeasure of Desire: The Science, Theory, and Ethics of Sexual Orientation.
2. There's also empirical evidence of former homosexuals choosing to become heterosexuals (e.g. here).
3. We don't choose how attractive or ugly we are, how tall or short we are, among many other traits and characteristics. Does this mean physical attractiveness and height are analogous to sexual orientation? If so, then shouldn't we legislate laws protecting ugly people and short people from discrimination by the film industry, the National Basketball Association, and so forth?
4. As Jeremy Pierce has pointed out in his A Realist Metaphysics of Race, there are various positions on what race is. Does race exist at all? Is race primarily a "natural kind" where "because of the genetic similarity, members of a race share the same range of moral traits, behavioral dispositions, and emotional dispositions"? Is race primarily a social construct? Etc. Thus, we'd have to first come to an agreement about what race is before we can make an argument from analogy regarding race and sexual orientation.
5. Perhaps LGBT advocates wish to tweak the argument so it's more like sexual orientation is sometimes but not usually a choice. If so, then it's no longer analogous to race if we take race to be what we are immutably born with.
Also, if so, then as Steve Hays has brought up in the past, people can be addicted to drugs, alcohol, smoking, gambling, pornography, etc. Many believe they can't always choose contrary to their addiction. Many can't help but sometimes or oftentimes indulge their addiction. Given this, I'd be happy to conclude LGBT sexual orientation is analogous to addiction.