And scientifically they are all unproven. You cannot say something is genetic unless that genetic source is verified. As I said, the studies done even hinting at genetic origins all conclude there is no conclusion. Most of them have not made it through a peer review without holes all in the argument. The major scientific, medical, and psychological associations all agree on that. Unless you have more credibility than these sources, I'm more inclined to side with them.
As for your machismo Mexican family example, are you saying that because they are ultraorthodox Catholic all of the offspring cannot stray from that belief? You say it's hard to imagine what environment would encourage homosexuality. Fill in the blank. This logic means any strict religious familiy should not have a drug addict, a murderer, an atheist, etc. etc. That's a flawed argument as well.
A friend of mine grew up in a family with 6 sisters. He was dressed up as a child by his older sisters, forced to participate in tea parties, etc. As he became older, he fit all of the stereotypes of a gay male - voice, walk, dress, the usual. He was teased, bullied, etc. He went through the whole debate in his head while being pressured by some gays telling him he HAD to be. Their argument was that he exhibited 'traits' that had to be from birth with no mind of his environmental upbringing. When this 'convincing' by others showed flaws he came to the conclusion this was a farce. He has no doubts about being straight. He thought it sad that others tried to convince him based on no evidence and flawed logic.
My step dad has a cousin who is gay. He does not know his father and was raised by his grandparents. All throughout school he dealt with being fat, ugly, nerd, loner, etc. He didn't play sports. He was bullied and some called him gay. Over a period of years, he heard it enough to start questioning if he was. He started hanging around gays. He felt included and far different than he did before. Long story short, he says he's gay, he's in a relationship, and is committing to his partner next month. He'll even tell you that he felt he was driven to believe this.
We can go on and on about examples. Still it leaves questions. Still leaves nothing scientifically conclusive, especially to start basing nationwide policies on.