Sorry, but I was "educated" BEFORE political correctness...in the 1950's and 1960's, before liberals took over...
anthropologically, there are gays in every culture...and since I've worked as a missionary in about eight cultures, I think I can base this on personal observation...
This implies inborn genetic reasons partly behind it, similar to other genetic behavioral problems (sociopathy, phobias, drug abuse).
Such things make one prone to certain sins, but people are free to give into temptations or not. That is where the "Choice" lies.
And the expression of such tendencies vary from culture to culture, due to social pressures. This is where I state the actions can be influenced by cultures. The observation of gays being from families with strong mothers and absent fathers goes back to the late 1880's...and Freud.
The argument of nature vs nurture on homosexuality and other personality traits has gone back and forth several times since I went to medical school...right now the "inborn" is on top, but thirty years ago, it was "developmental" causes...
Actually, it is probably both. But both early childhood influences AND inborn tendencies can interact in a person, and it is very hard for us docs to change these things once a person is an adult... for depression and phobias, prozac helps but doesn't cure...but psychotherapy and drugs can't do a thing for deep rooted homosexuality (as opposed to mild tendencies that are much more common)...
If a person could merely "chose" to be gay, he could be cured...and indeed, many can be cured. But NOT all can become heterosexual...some must chose celibacy...
"The number of men and women who have deep seated homosexual tendencies is not negligible. This inclination which is objectively disordered, constitutes for most of them a trial...Homosexual persons are called to chastity..." (Catechism of the catholic church)...
However, many who under certain circumstances have no access to women, or many who are bisexual can be seduced into the gay lifestyle...They can "chose" to enter into the heterosexual lifestyle...and their actions are greatly influenced by cultural standards, which is why the gay agenda to normalize homosexuality needs to be opposed: Because they will "recruit" many confused bisexual boys and girls into thinking that once you have performed a homosexual act, you are required to go into this lifestyle...(which is how the PC are teaching our children)...
FYI and reading pleasure:
http://www.freerepublic.com/focus/f-news/1420619/posts
Root Causes, Homosexual Consequences
http://www.drthrockmorton.com/idoexist.asp
I Do Exist
Just because their are, for instance, thieves and adulterers in every culture doesn't mean that such "tendencies" are necessarily inborn and they can't change. Everyone has differing temptations and weaknesses, although the human condition is pretty similar for everyone. People can change - if they want do enough.