Frankly the passages that are cited here within scripture are not really all that ambiguous. It is speaking of homosexual and lesbian behavior and yes, the acts are described as sinful. So too is heterosexual activity outside of marriage or adultery within a marriage. For that matter so is gluttony (which is usually waxed over rather lightly by the average overweight pastor in a pulpit (and lest anyone think I'm getting too personal, I was an overweight pastor earlier in my life and I'm including me in that grouping.) The list could go on of course.
I frankly believe that there is a significant apology owed by many churches and christians, not for calling sin what it is, but for the selective and hypocritical way that it has been treated and the singling out of one "class" of sinners over the others. It's really not all that different from the attitudes and actions of the Pharisees that Jesus condemned roundly for their willingness to don a mask and pat themselves on the back while condemning others. The message has been sent very clearly by many evangelical and fundamentalist churches that homosexuals are a special class of evil and therefore unwelcome even to visit their services and not to declare who they are unless they are there to repent or to give testimony of how they've been delivered. The message appears to be, deny who you are and clean yourself up first and then we'll allow you in.
That said, it's my belief that the most important thing, indeed the only thing that is vital is for people to come to Jesus Christ. Jesus accepts us where we are and the funny thing is that once we have accepted Christ and have the Holy Spirit within us, then these issues are things we can address as the Spirit brings them up and frankly, the motivation that is most effective is when we respond in love to whom Jesus is and gratitude for what he's done. That's far more powerful than the use of guilt and shame coming from other people who condemn others while they hide their own sins or shortfallings
Sexual orientation is a difficult thing for us to understand. To this point, at least to my knowledge, there has been no effective tie to a "homosexual" gene. Out sexuality is deeply personal and a part of our identity. It's a product of many different factors and it's difficult to know why we're attracted to whom we're attracted. I don't believe that homosexual attraction in and of itself is sinful or that a person who has that attraction is more of a sinner on the basis that they have that orientation. Most of what goes into making that identification within us happens at a level that is subconscious and not a volitional choice that we make. That said, as others have pointed out, it's what we do in terms of our acting out behaviors that is the issue.
Where the rationalization comes in is that the predominant moral system in our society and culture now, is not based upon the acceptance of moral absolutes but instead on a system known as Utilitarianism. Utilitarianism operates on the assumption that the greatest state that we can be in is that of "happiness." Therefore the measure by which things are "good" or "bad" is based upon the option available in any given circumstance that causes the least amount of unhappiness relative to the other options. It's this basis of thinking that suggests that things that Christians would say are wrong when looked at through the lens of Utilitarianism, begs the question as to who is really being hurt by these behaviors and if there is no victim then in what basis do we judge or cast others aside for these behaviors?
It's a powerful influence in the values that are taught in the post-modern, post-christian era that we're entering and it's seducing even to those who are Christians but don't recognize what is going on and so you have even Christians falling prey to this change in underlying value systems. It's no longer good enough for God to reveal to us what His norms are and what the purpose of His creation is. Can we bypass or circumvent these things? Yes we can and in the end if we're sincere believers, accepted by God through Christ, the grace of God is sufficient. However, there are still consequences and for the Christian who is either deceived in their own thinking or is outright rebellious there are temporal consequences for our actions and it will also serve to quiet or silence the voice of God's spirit in our lives.
This is true of all sin, not just the special "biggies" that we like to focus on because for most people the biggest sins are those sins that others commit and we're very willing and quick to give ourselves a pass.
Hopefully this isn't rambling too much, but the bottom line as I understand it is when we come to Christ it's vitally important to us how we see God. If we view God as the great "party pooper" in the sky who looks like Gandalf and hurls lighten bolts at those of us who who slip up then it's easy to see why we want to put on masks before God and other to convince them (and ourselves) that we're OK and "good boy and girls" who are toeing the lines. When we see however the Father that Jesus came to reveal to us and tell us that God is loving and accepting (think the loving Father in the prodigal son parable) then we're free to drop our masks and accept that God accepts us where we are, that we can accept one another where we are and we can learn what it really means when Paul assures us (and this is worth printing out in full so here's the first part of Romans 8 that speaks to much of this:
Rom 8:1 Therefore, there is now no condemnation for those who are in Christ Jesus, 2 because through Christ Jesus the law of the Spirit who gives life has set you[a] free from the law of sin and death. 3 For what the law was powerless to do because it was weakened by the flesh, God did by sending his own Son in the likeness of sinful flesh to be a sin offering.[c] And so he condemned sin in the flesh, 4 in order that the righteous requirement of the law might be fully met in us, who do not live according to the flesh but according to the Spirit.
5 Those who live according to the flesh have their minds set on what the flesh desires; but those who live in accordance with the Spirit have their minds set on what the Spirit desires. 6 The mind governed by the flesh is death, but the mind governed by the Spirit is life and peace. 7 The mind governed by the flesh is hostile to God; it does not submit to God’s law, nor can it do so. 8 Those who are in the realm of the flesh cannot please God.
9 You, however, are not in the realm of the flesh but are in the realm of the Spirit, if indeed the Spirit of God lives in you. And if anyone does not have the Spirit of Christ, they do not belong to Christ. 10 But if Christ is in you, then even though your body is subject to death because of sin, the Spirit gives life[d] because of righteousness. 11 And if the Spirit of him who raised Jesus from the dead is living in you, he who raised Christ from the dead will also give life to your mortal bodies because of[e] his Spirit who lives in you.
12 Therefore, brothers and sisters, we have an obligation—but it is not to the flesh, to live according to it. 13 For if you live according to the flesh, you will die; but if by the Spirit you put to death the misdeeds of the body, you will live.
14 For those who are led by the Spirit of God are the children of God. 15 The Spirit you received does not make you slaves, so that you live in fear again; rather, the Spirit you received brought about your adoption to sonship.[f] And by him we cry, “Abba,[g] Father.” 16 The Spirit himself testifies with our spirit that we are God’s children. 17 Now if we are children, then we are heirs—heirs of God and co-heirs with Christ, if indeed we share in his sufferings in order that we may also share in his glory.
So the answer to these types of issues are not to do what we're so humanly prone to do and make lists of sins and rank them and put together our human programs of how to clean ourselves up and present ourselves to God. The answer is to surrender to God and His spirit and enter into a loving relationship secure in who we are in Christ and then allow God to work these things out in our lives. Many of these things are life-long processes and we're doing nobody, least of all ourselves, any favors by trying to go back to the old taskmaster of self-improvement and self-discipline as the foundation to any change in our lives. It's doesn't work and it's no longer necessary. When the Spirit of Christ dwells within us we can count on God taking care of things in terms of guiding us into truth and maturity. Those elements may well end up being a part of change that is brought about in our lives but to the extent that it is, it is secondary to the work of God's Spirit in our hearts and lives.
So, for me, I love those who are homosexual, bisexual, heterosexual and even monosexual because God loves all of us and I'm no better than anyone else and certainly no better than God. I will agree with scripture with regard to what is says about homosexual behavior but I'm not going to make some sins less and some sins more in the eyes of God. Yes I understand that our human values and legal system makes such distinctions. That's fine. My citizenship lies elsewhere and if God can work through sinners like the murderer and adulterer King David, incestuous relationships in the Old Testament (some even within the human lineage of Christ) and more importantly, my own failings then I will start there and believe that God is equal to the task of bringing others to the point of addressing their issues and rejoice that they, like me, are not loved based upon their performance.