When I'm defending the traditional Christian stance on homosexuality, my go-to passage is not Leviticus 18 or 20. Nor, as a matter of fact, is it Romans 1.
I'll often approach the topic more from a Genesis 1/Ephesians 5 perspective -- God's designs for marriage and sexuality being paramount. However, what I constantly run into is the popular argument that Leviticus 18.22's language invokes the type of sexual violence common in the time period, which would render the English reading something more akin to, "A male shall not forcibly lie with another male, as such sexual violence is an abomination."
This understanding of the subtext, while maybe not entirely inaccurate, still misses the overall context of the chapter. It also ignores the fact that the Hebrew word translated "lie" in English to connote sexual relations, does not here carry any violent overtones. In fact, the word translated "lie" in other Old Testament passages might have the same root, but with a different connotation when elsewhere used to connote violence or ambush (i.e. "lying in wait," as per Deut 19.11; Prov 1.11).
That said, of course rape is not a modern sin and it is not dis-included from the sexual sins addressed in the Pentateuch (see Deut 22.25). In fact, many of the sexual deviancies listed in this passage and others would likely involve some kind of violence. Actually, I'd argue that all of them do. After all, incest is most often the result of one family member taking advantage of another or using him/her against his/her will (see Judah/Tamar [deception] -- Gen 38.12-26; Lot and his daughters [deception, drunkenness] -- Gen 19.30-38; Amnon/Tamar [forcible rape] -- 2 Sam 13).
I'm not saying that there aren't plenty of cases of consensual incest, of course. Sin is tempting and seemingly justifiable for all sorts of twisted reasons. I'm also not arguing that violence is a moot point when it comes to these sexual sins. What I am arguing is that, if the issue at stake in Leviticus 18 were simply violence, and that the practice of homosexuality itself was acceptable on non-violent grounds, then we would be forced to say -- by that same standard -- that incestuous sexuality was also acceptable, in the case that both parties were consenting. In other words, we can't just pigeonhole one act in this list as being explicitly violent, therefore rendering it acceptable in non-violent circumstances, and not also apply the same logic to the rest of the passage.
Ironically, this is not the perspective our culture holds when it comes to this passage -- obviously, incest is wrong (or at least not preferable) because we find that type of sexual expression unhealthy and distasteful. Nobody marches for the rights of incestuous couples, even though there are state and national laws prohibiting legal unions between siblings and parents/offspring. However, because our culture wants to endorse the practice of homosexuality, the caveat of forcible rape is applied to this passage to suggest a loophole that doesn't actually exist.
The larger context of the book of Leviticus is even more compelling. The entire text resounds with the theme of God's holiness, emphasizing again and again the importance of the Israelite people living with radically different beliefs, customs, laws, and ethics than the nations surrounding them. Specifically in Leviticus 18, the topic is sexual sins that were violations of God's standard of holiness for Israel. As with the rest of the book, the laws He is here ordaining will separate His sanctified people from the practices of the foreign nations. Specifically included in Leviticus 18 are incestuous acts, bestiality, sex during a woman's menstrual period, child sacrifice, and homosexuality. The child sacrifice thing particularly seems out of place here, but the ritualistic sacrifice of children in the pagan Canaanite nations would definitely involve lewd fertility rites, and would symbolically defile maternity, paternity, and one of the divine purposes of copulation.
Again, sexual coercion or outright sexual violence is implied in nearly all the acts listed here, which is not excusable or unimportant. But the central thrust of this passage is the bigger theme of violating God's standard of holiness -- regardless of how, when, or why they take place. In other words, what do all these things have in common? They all break God's design and defy God's purpose. There are no specific details or conditions given for any of these practices, which means there are no circumstances that would render the act in question acceptable, and no circumstances that might provide a convincing case for the Almighty's approval. In fact, the only "favorable" conditions in this text are deliberately removed from consideration -- that is, when it comes to a man taking his stepsister as a sexual partner, regardless of whether or not they grew up together, which is probably the only time we might culturally consider the incest to be a mere technicality and argue for its acceptability (18.9). In that instance, there most likely wouldn't be any violence taking place, but it is still an act condemned for the standard it violates.
Bottom line, Leviticus 18 removes the issue of motive entirely and makes the blanket statement that any engagement in these types of practices is a violation of holiness. For Israel to do any of them would be for them to live like the foreign nations, whom God was chastising for the very same sinful acts. Such a disregard for holiness within the Israelite community would result in excommunication or death. What is ultimately important, therefore, is that the specific conditions of the act in no way alter the fact that it is still sinful.
I'll leave it at that, because today's standard of what constitutes acceptable sexuality can't be determined by just what the Old Testament says about sexual conduct. We can only dispel arguments that seek to prove homosexuality's acceptance in history, so that such twisted logic doesn't become a platform for modern acceptability.
Jesus certainly didn't come to eradicate the Law -- He came to fulfill it -- but He also came to inspire within us not a duty-bound obligation to rigorous customs, but a love for the same kind of holiness that God has always required of His people. There is no way to reconcile any act -- that is still inherently sinful under any circumstances -- with a God whose perfect character demands perfection in His children.
And that's why the message of the cross is so potent.
The cross communicates that God loved us enough to buy us back from our enslavement to sin, at the cost of His own blood. The cross communicates that there is a much greater consequence in store than any shade of loneliness or despair in this life can possibly foreshadow. The cross communicates that none of us were able to fix our own problems, but that Jesus came to give us the power to make that possible.
The cross communicates that homosexuality is a sin you can be rescued from. You are not beyond God's mercy. Repentance is not out of the question.
The cross communicates that a far greater fulfillment awaits those who come spiritually hungry to the Lord than any human relationship can offer.