Personally I doubt it's anything more than slightly genetic because nature is a relentless bitch who have suppressed genes for far less than making 5% of a certain population explicitly being turned off by the opposite sex and therefore reproduction. Yeah, gay uncle hypothesis and all of that but I'm not sure considering the survival rate to adulthood wouldn't be exactly high among human populations in the wilderness.
I tend to agree with the theories concerning psychological and social factors because people's personalities change with time, sometimes dramatically so, and sexuality could be considered a reasonable part of the human psyche and therefore subject to the same changes. This and predisposition due to hormonal exposure in the uterine environment.
