The homosexuality issue is slightly more complex than your understanding of it. While there may be some element of choice to some degree, what is important is that many people, probably most people, feel that they can't change their's. Most straight people feel that they couldn't choose to be gay, and would be upset if people blamed them for "choosing" to be straight. They would feel it was unfair and discriminatory, because while it is perfectly fair to criticise people for their choices it isn't fair to criticise them for things they have no control over.
So actually, the science of it isn't even that important. What is important is that most people can't choose to be straight or gay, they just are, and people who blame them for that deserve criticism. I think most people understand that, but somehow you got bogged down on one specific detail and missed it.