Hmmm. Well I think the idea that the New Testament does not condemn homosexuality is flatly ridiculous. I do realize that there has been an article here and there in support of the point you are making (e.g. the one by L. T. Johnson) but for the most part I understand that those supporting your stance feel that they are the prophetic voice that is taking its starting point with the Bible and are moving on from there. An outstanding scholar, John Milbank, who supports your overall position also says: “Although I favor the gay cause, I actually think the conservatives are more or less right about the Bible” (http://www.pbs.org/wnet/religionandethics/week707/commentary.html)... I certainly agree.
I still don’t see why you would think of incest as immoral. Why from scripture would someone being born heterosexual be prevented from having a deep and committed love relationship with their sibling which they also felt was before God and in the light? I do not think you can say they cannot have such a relationship without appealing to the dos and don’ts of scripture which you are so aggressively trying to avoid. You seem to feel that these laws which God gave (in the NT) can be tossed aside as long as you have some subjective sensation that you are “speaking before God in the light.” You appear to be randomly cutting out all things that sound like law and calling them legalism. What do you mean by legalism? Having a law does not make something legalistic. Legalism is following laws outside of empowerment from God’s Spirit. There is nothing wrong with following commands as long as you do not believe that you are somehow justifying yourself by following them (1John 5:3f).
Also, about your opening sentence: “In answer to the question John poses to me, the overarching principle is more than a loving, committed relationship. If this is the standard, then "adultery" would also be acceptable, which is a violation of one's commitment of love to their spouse and is sin on this basis, which was addressed in the Ten Commandments.” Obviously if one commits adultery then they are not in a committed relationship so I don’t see your point…and there you are appealing to laws when they fit your purpose.