Backing up this claim: Some people grow out of religion, or find it isn't right for them (expectations, world, counter-beliefs etc etc). Sexual orientation is on the opposite end of the scale. It's difficult/impossible to change your orientation, it's part of your personality.
The born with or grown up with argument is interesting, as there is no hard, scientific evidence to support either of them. You could say that sexual orientation is not something you are born with, but is something that you understand fully when you reach the right age where you understand sexuality - but not in a society/growing up sense where the environment effects who you are and what you do. A sort of middle area where both age and genetic/impulses collide.

