I think its a combination of many things or maybe one or a couple of these things:
1. Childhood experience (Abuse or otherwise)
2. Neurological condition involving a difference in brain connectivity
3. Biological condition (Set by genetics or as simple as diet)
4. Social acceptance (Not everyone sees things the same) which involves choice
That's just my view. I feel not all cases are the same.
Gay by circumstance should also be an option to consider. Someone may not be biologically gay but placed into a situation that makes them act out with the same sex. I don't know if that makes sense but you know its not all by choice or by being born that way.
Weather it happens by choice or in a natural thing, it is still happening and there are gay people. They are still human, eat, breath and love. So treat them with love and kindness like you would anyone else.
Comments: Homosexuality is all mental and not physiological. Therefore, its easy for the cause to be a number of factors. The brain's wiring, distress growing up, cultural acceptability, etc. It isn't one thing. I agree all should be accepted. You do not have to like it but you should not lose respect either by being hateful.
I don't think it really matter if people born gay, gay by choice, or something in between. The key word here is people. We should give everyone the respect we feel we deserve. As long as someone isn't doing something to hurt others then we should let them live their lives.
People are born this way, its all biological the same way you may feel attracted to the opposite sex there are some who feel attracted to the same sex. There might be a very small percentage who turn gay but maybe their biological makeup changed with time.
I think we are all born neutral and over time and experiences your biological make up changes over time. Whether it is internal or external influences people will turn out the way they turn out. I think a lot of this has to do with ones biological make up which can change over time.