I agree with you that there probably is a biological predisposition to homosexuality -- in most cases. But I'm always baffled be people framing it as either "born that way" or "choice." It could be neither one. Has everyone forgotten Sigmund Freud? People can have things happen to them early on that condition their brains a certain way. For instance, a woman who grows up with an abusive father may subsequently be attracted to abusive men. She is not "choosing" to feel this way but was not born this way, either. Rather, her brain was conditioned at an early age.
Regarding cultural factors, in the book "My Genes Made Me Do It," Neil and Briar Whitehead refer to a 1952 study by Ford and Beach that examined homosexuality in 79 cultures and found that the behavior varied from culture to culture, with it being rare or absent in 29 out of 79 cultures. And in the 1994 University of Chicago study "Sex in America," the authors concluded that culture played a much more important part in contributing to sexual behavior than is generally believed. So there may well be an element of learning in sexual behavior, as there is in other behaviors.
Interesting reference. My whole point is that studies are still ongoing and to the best of my knowlege still inconclusive. Most reasonable people understand that while some cultural influence may be present, it doesn't explain the Cheney, Terry, or Keyes children, all of whom were raised in strong Christian homes. I am reasonably sure it's not a choice, or why would the daughter of Dick Cheney choose to be a lesbian. But I certainly don't know what it is.