That's an important point many talk right over. I think if people slowed down long enough to discuss the issues, there would more light than heat generated and I also think many or most would agree with you.
Where the confusion stems, I believe, is that many mean the behaviour is a choice, not the same-sex-attraction and when they don't clarify their position they lose some of their audience.
Now, I have to clarify something myself. When I say same-sex-attraction isn't a choice, I mean that for most cases. The only reason I bring this up is because there is an adamant group who claim to have chosen their same-sex-attraction. I'm referring to the Queer by Choice group.
For the vast majority of those with same-sex-attraction, I believe the evidence supports it's not something they choose, but at the same time they are not born-that-way. It's not a topic that can be easily understood with only a cursory look at the evidence.
“Where the confusion stems, I believe, is that many mean the behaviour is a choice, not the same-sex-attraction”
I can accept that. These conversations frequently devolve into silly arguments due mainly to misunderstandings. When it starts getting rude, I generally shut up and go away. I don’t worry enough about the subject to want to fight about it.
The US is a presumed heterosexual society. The presumption is that we are all going to be straight: our parents, family, friends, acquaintences assume as much from the day that we’re born. We therefore all start as straight; that’s why you don’t hear of anyone choosing to be straight, because for all intents and purposes, we’re all “born” straight. When environmental forces (conscious or not) change our socialized preference, that’s when people become/choose homosexuality, bisexuality, etc....