God damnit, you pop up in these threads all the time.
One way to see it, the world has imbalances. Homosexuality may have little to do with genes, but still involves biological differences. Say you take too much of a drug, you could overdose and die. If you are exposed to extreme amounts of radiation (practically any kind) you can get side effects, such as cancer. If you eat healthy foods while you're pregnant, generally, it is healthier for the fetus as well. Have a wicked pituiatary gland? Who knows, you might grow to be 7ft tall.
Now imagine, while a fetus is maturing in the womb, there is an imbalance in horomones, say too much estrogen in a developing boy. Not much, but an imbalance no less. As the child devlops in the womb, this horomone imbalance could cause changes in the fetus, perhaps altering the devlopment of the hypothalamus. This could seriously affect the life of that child. Although still fuzzy, this is very plausable, and the hypothalamus could be largely responsible. You could duplicate it in animals. Nature vs. Nuture is fucking powerful, but usually, Nature wins (so you could try to raise a girl a boy, but that girl may reject that way of life because it goes against the engraved biology. Look into John Money for such examples.) So yea, slight developments against the norm (not in a slandering type of way) could essentially create a homosexual. It doesn't have to fit god's plan for procreation. Just a thought.
As for the question of the thread, yea i think gay marriage is fine. Why shouldn't it be? This is a secular nation. Not to say religion has no role, but using one religion's parameters shouldn't be done. There are billions of people who are not Christians, so should be barred from getting married married? Some may choose to get married in religious observance, but many get married for the binding elements. Hold religious views is fine, but don't use that as discrimination against others.