Because one's broader view of Morality does effect how open one will be to the Homosexuality issue. I think to many traditionalists that partly justifies their not even listening to the argument.
Because even when the Clobber Passages are properly understood, viewing it as totally okay to be a practicing Homosexual or Bisexual requires at least one of two major assumptions about Biblical Morality to be wrong. 1. That all Sex outside Marriage is a Sin. 2. That Marriage is only between Men and Women.
I have argued on this Blog quite strongly that The Bible does not Condemn all Sex outside Marriage, and that the word Fornication refers to Prostitution. And the origins of condemning Sex outside Marriage lie with Plato. It helps to understand my Ye Hath God Said study before reading those, to open one's mind to rejecting the assumption that of course God is super strict and questioning that is clearly a tactic of Satan.
Now I do not want Biblical Marriage to define Legal Marriage. I'd prefer the Government didn't give out Marriage Licenses at all. But as long as they do I want all alternative forms of Marriage to be legal, Gay Marriage, Polygamy, Polyandry, Polyamory, Group Marriages ect. As long as everyone involved is consenting and an adult, the State should not be allowed to restrict it.
And I feel Christians should refuse to get Marriage Licenses from the Government regardless, for the same reasons I support the House Church movement and rejecting the 501c3 status. As I explain in The State, The Church and Marriage, There is no Marriage Ritual Ordained in The Bible and Marriage License vs Marriage Covenant.
Some Gay Affirming Christians take the opposite approach. I understand why.
1. They don't want their love to be viewed as different from Male-Female love. Marriage should not be necessary to achieve that, David's greatest love was Johnathon, regardless of only being married to women.
2. Some want to stick as close as they can to an Augustinian Sexual morality to avoid the stereotype that Gays and Bisexuals are deviants and perverts, that condoning them inevitably leads to anything goes. Thus we get Dan Savage bragging his husband being a "stay at home dad", and Yuri critics like Erica Freidman over reacting to even the mildest forms of Incest.
But I feel history shows the greatest gateway drug to perversion is being too sexually prudish. When you tell people they're sinning anytime they don't wait for a long term commitment, and shame them for it, it frequently leads to them questioning any restrictions, even the basic idea of consent. That is again one of the points of my "Ye Hath God Said" study.
Allowing Sex Outside Marriage does not automatically lead to no morals. As long as people try to stick to the Golden Rule, and Christians always seek the guidance of The Holy Spirit. The right decisions can be made without needing to bind people to the minutia of a rule book.
However, since I believe we are not under The Law, I will never condemn or shame any Gay Christians for practicing a Gay Marriage. We are under The Law of Liberty now, which is flexible.
My point here, is that in trying to open peoples minds on this Subject. I think it's often necessary to begin with Broader issues. Then once that is achieved it may be easier for them to accept that what they thought they knew about the Clobber Passages is wrong.