See Saboteur's post above, where he talks about his two, homosexual brothers.
Do you genuinely think that someone would choose to be gay, when society treats them like they are abnormal, disgusting, and the like? Living a straight life is easier, don't you think? Maybe those who decide to get married and have kids have taken the easy way out or they are doing it for reasons other than that they decide they will be attracted to the opposite sex.
Take my godmother. She has a daughter who was unquestionably gay but she never came out to her parents. She had a party, which she invited her parents to (and my parents) and my mom said that this was clearly Wendy's "coming out" party. However, after the party, people started treating her differently. They had hunches that she was gay (she fits the stereotype), but the party confirmed it. Wendy has now married a guy, and I cannot believe it. My mom (who is rather naive when it comes to this) says that Wendy is heterosexual. I doubt she is, although she is living as though she is one.
Anyway, my point is that Wendy has chosen to live a heterosexual life, and the acceptance she has received from those who treated her differently after her party is shocking to me (but in a disgusting sort of way). So for some, it's about fitting in.