quote "the homosexual orientation is not chosen and, therefore, is not sinful in and of itself"
rofl!
So I guess people born with the need to kill people aren't committing a sin either since they didn't choose to be born with the need to murder people.
According to most Christians, no, they're not... unless and until they act on that need. Note the quote. "The homosexual orientation is not chosen and, therefore, is not sinful..." It doesn't say "The act of homosexual fornication is not chosen and, therefore, is not sinful..." They're saying you can't choose to whom you're attracted and so won't be held accountable for that... but you can choose what to do about your attraction.
Put another way, since fornication between any two people is sinful, being attracted to another person of the same sex is just as sinful as being attracted to a person of the opposite sex to whom you are not married.
You don't sin, according to the popular view, until you actually commit a sinful act.
Of course, Christians with this view aren't familiar with Matthew 5:28. Those that are realize that all lust (heterosexual or homosexual) is sinful, that all of us are guilty of it, and that we all need God's forgiveness.