Exactly.
Well, let's be clear on the definition of free will...as I am not trying to get into a religious predestination discussion here.
I am making the assumption here that you will agree that God has given Man a few moral laws, including a prohibition against homosexual acts.
So, on that assumption, and realizing that all mankind, including even Jesus, are subject to temptation, Free Will is the ability to act on those temptations and sin, or reject them.
So even if homosexual lusts are genetic, or occur during the development of the fetus, or in events happening in early childhood, we have no more excuse for giving in than we do for any other type of fornication, also forbidden by God to homosexuals and heterosexuals alike.
Now, there are other ways to argue against homosexual practices, but Free Will is a fundamental religious concept, so that is how I choose to argue it.
The same argument would apply to any other sin, or moral decision. We don't have to give into our dark desires. We may not be able to keep from having them.