Whether homosexuality is a choice or not is irrelevant. God originally designed sexuality to be expressed between one man and one woman in a family unit. (e.g. Adam and Eve) When humanity fell, everything got corrupted, and man became hostile towards righteousness and given over to depravity. As far as God is concerned, you are either fully justified or fully condemned; there is no middle ground between the two.
Regardless of how you sow to the flesh, you are going to reap corruption. Homosexuality is just another sin of the flesh, and some people are merely more susceptible to it than others, just as some people are more susceptible to violence, rape, or stealing. (although some sins are worse than others) People who are straight are really no better off because they are merely enslaved to something else, even if they aren't aware of it.
God has been saving people throughout human history, long before Christ came. (such as Adam/Eve, Moses, Enoch, David, Elijah, and many others) Christ had to come so God could be justified in saving people, because otherwise how could a righteous God show any mercy to sinful people without being unrighteous? God dispensed swift and immediate justice to Satan, yet showed mercy to humanity. In a human analogy, you would probably consider it unjust if a judge pardoned (on a whim) a convicted murder who had been found guilty by jury.
As the progeny of Adam, every human is born into sin by default, and has no hope of escaping condemnation apart from God's mercy. Man originally had a full understanding of and harmony with God (Adam and Eve regularly communed with God prior to the fall) yet immediately after the fall, Adam and Eve ran from God in terror. Although God was merciful by sparing Adam and Eve, (while delivering the promise of Christ) man has been separated from God ever since, and Christ is the only bridge that links God with man. If not for Christ, I (and all other Christians) would have no salvation and God would have no choice but to destroy me and everyone else who has ever lived.