Until you can prove via gentics that what you say is true, you won't ever win this argument. Some gays just are, some are the products of their childhood environment, and some are gay because it is now "cool" somehow. I don't know what the proportions are, but I believe the later two categories far outweigh the first.
I'm not going to argue this poinwith you as this is your opinion and you're not likely to change it, however I do want to provide additional perspective.
I appreciate how you do concede that some do not have a choice in their sexuality - that's a better position than many in opposition hold.
Also, while there are no conclusive studies right now there are several which seem to indicate differences in brain chemistry, and presence of certain genetic markers in gay folks. I understand there has been no 'gay gene' discovered, but research indicates homosexuality is more a combination of genetic markers along with envirnmental factors in the womb (hormonal exposure). Nothing conclusive, but there has been progress there.
I can only speak from my own personal experience and the (many) gay folks with who I have discussed the topic, but want to add additional perspective.
My brother and I are both gay, and neither of us have ever felt attraction to women. As I mentioned earlier in this thread I fought against it for years, agonizing and painful years. No matter how much I wanted to be 'normal', it never happened. Not with prayer, counseling, nothing. So I am 100% sure that my sexuality is innate.
In addition, I have met a lot of other gay folks over the last 20+ years in which this very topic has been discussed. The overwhelming majority all state the same experience - they have always had the attraction, it was never a choice for them. Bisexuals are obviously a different situation, so I'll grant that they might be a good example of choice. I'm not bisexual so I have no idea what that's like. I'm 43 now, and if you heard some of the stories for gay folks who grew up around the same time I think it might adjust perception a bit. So many ridiculed, disowned by family and church, physically absused, constantly told how they'll be burning in hell. Why would anyone choose that? Obviously we all didn't have those experiences, but I have been surprised at how many did.
I currently work with a charitable organization for LGBT youth and their allies. While society is much better today for gay people, I am astounded at how many of these kids are still being disowned and bullied by their families and peers. It's easy to see why the suicide rate in gay teens is significantly higher than their counterparts; it's not an easy life, even today.
I don't expect this to change your opinion, but please understand this is sharing views from the other side of the fence. In dealing with a large population of gay people directly, their experience says that it is very much something that is innate.