What's With Xians Insisting That One Chooses To Be Gay, So They Don't Get Certain Rights?

For the sake of argument, let's stipulate that one chooses to be gay. What's the problem with that?

Isn't being a Christian a choice, a choice that gets made for you by your parents, but a choice that you can make for yourself later in life? Last I looked, you can choose to change your religion or your religious sect every day of the week, and nobody is going to say that your having such a choice threatens your right to religious freedom, or to any other civil right bestowed by the Constitution.

So one must ask - IF being gay was a choice, why would that call into question a gay person's right to any civil liberty, including the right to marry whoever one wants, regardless of gender?