There have been scientifically documented cases of birds (seagulls and penguins specifically) exhibiting homosexual behavior. Is there a homosexual penguin agenda? Do seagulls choose to be gay?
In terms of whether someone chooses to be gay (assuming you're trying to make a point out of that), I don't think that that should really influence the debate on whether gay marriage is right and/or should be legal. From my point of view that's like saying someone with a tendency to steal or someone who's insane killing someone has the right to do so because they didn't choose to be insane. Not that I'm comparing gays to murderers or thieves here.
There. I said it. Forum, feel free to attack me.