The problem with this argument, on both sides, is that they want to lump ALL gay people into the same category. Gays want it seen that they are ALL born that way, those opposed want to say that it is a choice for all of them. I think there are varying degrees. The partner of this woman is someone who I think became gay from her life experience, and thus it was something more of a choice, but by some strong anti-male experiences she had from her past.
Here is another problem with these arguments, this idea that if it is a "born" thing, that it is Genetic. This doesn't have to be true, I really doubt there exists a "gay" gene. _IF_ some are born this way, I think its probably an error in the expression of the genes, a birth defect.
It's complicated, but I think you would change your mind if you read more on the subject.