A <em>substantial</em> body of scientific evidence suggests that it sexual orientation is mostly biological. I could start listing the stuff, but just a few moments of Googling will allow you to find it yourself if you're actually curious.

However, I don't know why it's even relevant. Whether homosexuality (or a/demi/bi/pansexuality) is a choice or not should not remotely affect behavior toward it. Mostly everything we do is a "choice" (depending on what notions of free will you adhere to). It could be conclusively demonstrated that homosexuality is 100% consciously-chosen, with absolutely <em>no</em> influence whatsoever from environment or genetics, and that would still mean absolutely nothing in regards to whether or not gay people should be conferred the same privileges and protections as straight people.

So what's your point? You say that X is a choice unless it isn't a choice. I could just as easily say "I think that OBESITY is a choice unless its anatomically, biologically and genetically uncontrollable." I have not demonstrated, or even attempted to demonstrate, whether obesity <em>is </em>genetic or conscious, and even if I did prove one way or the other, it doesn't follow that I should therefore discriminate against fat people...

Homosexuality can't be anybody's natural choice, but it is an illness.  There is a certain private body part that is naturally designed to be an exit point for feces and intestinal gas instead of being used as an entrance point for a penis and sperm.  Nobody chooses the risk of getting AIDS and hemorrhoids. 

It is not a choice, it is a kind of disease. They should be cure properly. Because their choices are opposite of human creation due to they couldn't keep going on human generation. If we accept and legalize this kind of choices, we would be terminated ourselves as a human beign.  They can be funny creators, they can be specials, we could treat fairly and tolerable themselves, but they can not accept them as normal human beigns and legalize their choices. 

I don't understand this argument. So people have sexual desire for the opposite sex yet they choose just to have relations with their own sex - why?

I mean really if you look at the difficulty it causes people to come out it makes no sense. People have lost their friends and family because of it. Do you really think they choose that? Not to mention the suicides from it.

Despite that even if it was a choice so what? People should be free to choose how they live. I think people should be less concerned about regulating the lives of others and concentrate on themselves.

You have asked a very serious question. I am happy to give you my  respectful opinions.

1. I think that many non-homosexuals dislike or fear homosexuals because:

a. Many non-homosexuals know that many famous people in their own country are homosexual or bisexual.

b. Many non-homosexuals know that some of their family members or friends may be homosexual or bisexual.

c. Some non-homosexuals are afraid that they, too, may feel an attraction to the same gender.

2.  I also think that homosexuals have a responsibility:

a. Homosexuals should realize that the word "marriage" is very important to non-homosexuals, so homosexuals should let the non-homosexuals keep that word.

b.  Homosexuals should not have "gay pride" parades, for that just makes a lot of people angry and afraid.

c. Homosexuals should be very careful in intimate situations to make sure that they do not spread HIV.

3. I believe that there are some countries (I will NOT name them) where homosexuals and non-homosexuals live together peacefully.  That is, the police do NOT hurt homosexuals; homosexuals lead very QUIET lives. Nobody talks about the subject. People live and let live. Sometimes silence is the best policy.