Getting back to the initial post...
Well the Christian folk who now in the nature vs nurture thing, huh?... Many fundamentalists still believe that ppl willed theymselves or were "corrupted," recruited, etc into being gay. The Catholic church says it's a "condition." I presume they would quietly add the word "mental" in front of condition if pushed.
Personally, I believe it's 98% genetic and 2% social factors which no one seems clear about. Oh, they've mapped the human genome, but a geneticist told me they will spend the rest of this century trying to figure out what those genes do...
The movie seems to sorta imply a nurture thing with Jack and Ennis both having distant (that might be to kind to describe Jack's dad) fathers. Don't really know about Ennis's father but the nurture debate would say EARLY childhood influences (when Ennis's dad was alive) influence sexual orientation.
However there are many gay men who come from high functioning families and there are many straight men who come from a household without a father present. I would presume the same would apply for gay and straight women. The Cheney household might give me pause for thought, though.

350 posts, hah. Gawd, how can a thread get that long?