Its not that much a disagreement, we know its not genetic, identical twins can split on the issue. As far as the in utero, I saw it on a study, that maybe at a particular time in development there is not enough of some nutrient. This is not any different than trauma to the developing child. The time frame would be short enough to explain the frequency of the homosexual in the population as a whole. And would also explain the homosexual without any known abuse or abnormal parenting.
You can be sure that determination of the cause of homosexuality will not be as exciting to the left as it will be to the right. In fact, looking for such a cause is probably very non-pc. But I don't care. Take care.
Studies involving identical male twins find that if the one twin is gay, the probability that the other twin is gay is 38% (if I remember correctly). This doesn't sound like much until you realize that only 2-4% of the male population is homosexual: so the probability that the identical twin of a gay man is gay is ten or more times more greater than normal. The same number for left-handedness is only 1.5 times more likely (8% of the male population is left-handed, and if a left-handed man has an identical twin, the twin has a 12% chance of being left-handed).
But of course, even though there appears to be a strong genetic component to homosexuality, it is certain that it doesn't cause homosexuality, it only increases the odds.