...and a number ten size can of worms is opened
There are so many issues here. Homosexuality and religion. The Bible. What exactly marriage is.
Let's start with the whole religion and sexuality thing. First off, the Rabbis have gone over this thing longer and in more detail than any Christian theologians. What have they concluded? The only such act that is actually scripturally forbidden is, umm, the insertion of tab "A" into slot "C" by one man on another. Other things including all lesbian activities and all other male-male stuff comes under the vague catch-all of sexual immorality, mostly rabbinically prohibited. To put it bluntly, the really terrible thing to their mind was for a man to be someone's *****.
Back in the day marriage wasn't really about love. It was about property. It was about land and flocks and alliances between families. It might be about having a beautiful wife. It wasn't about romantic love. That sort of passion was considered all well and good in its place but hardly a matter for so important a civil contract. As they said "marriage without love leads to love without marriage". Mistresses, concubines and prostitutes were very common. Even in recent times (cf.
The Way We Never Were) most men had their first sexual experience with prostitutes and by some measures most of their sex period.
Things we would call erotic friendships between women from "old school friends" to Boston Marriages were more or less common. But since it didn't have anything to do with a man taking the subordinate female role and no pregnancy was possible it just wasn't as important culturally.
In fact, "homosexuality"
per se is a fairly recent invention. There were men who preferred boys or men, women who got their passion from other women. Some acts were tolerated or prohibited depending on time and place. Was the love of David and Johnathan deep, abiding and possessed of an erotic component? Almost certainly. Was David the king and could get away with a lot that regular people couldn't? Definitely. Was it "homosexual" in the modern sense? Depends on how you define it, but they wouldn't have thought of it that way. A man might have his closest emotional (and maybe physical) relationships with another man, but marriage was a matter of business between a man and his wives' families. Yes, I'm still wondering why the Christians got rid of that particular custom.
Marriage? I alluded to "Boston marriages". They existed under one form or another for a long time and were socially acceptable in several more religious times. But marriage was always at least as much a civil and financial contract as anything else. Dowries. Bride-prices. Obligations to support children. Family status in the case of the death of one of the parties. The Best Man marrying the bride if the groom died before the ceremony. The sin of Onan. Primogeniture. The household as the fundamental economic unit.
In fact, it seems that the medeival Catholic Church had same-sex union ceremonies that were not exactly marriage but were darned close. They don't quite fit into the single-size religious and civil contract we have now.
So what is marriage? What should it be? It has gone through more forms than you can imagine all over the world through history. Generally it has supported the economic form, encouraged social stability, conserved capital and provided for the well-being of any offspring. The confusion comes when the civic/civil/economic gets conflated with passion, eroticism and affection and the Church (anyone's Church) gets layered on top of it.
I would say that clarity is important. Insofar as marriage is a religious thing, keep it out of the laws and the laws out of it. Let the churches mumble the words over those whom they choose according to their rules. By the same token, mature competent adults should be able to enter into contracts with each other. If that contract doesn't meet with the approval of the Church, fine. The Church doesn't have to approve it, and the participants don't have to attend that Church.
Sex and passion? Men and women have been fumbling around and making any variety of mistakes and arrangements for a long time. Whatever a man, a woman, and another woman with dangly bits want to do with a troupe of acrobatic midgets is their business, not mine. They probably will anyway. If a particular religion doesn't endorse it, fine. The pervs don't have to approve of them.
But the idea that the contractual aspects of marriage and the erotic and the emotional have to conform to the religious muddles and confuses things. Society will not fall apart if people are allowed to arrange these things for themselves. And as things change different arrangements will inevitably arise to better suit the times. My pastoralist ancestors lived much different lives than the desperately poor
lumpenproletariat of the Roman Empire out of which Trinitarian Pauline Christianity arose. The requirements of an agricultural lifestyle were different again. Now we're back to the cities, but this time we have low infant mortality, contraception, longer lifetimes, and women whose sole economic value isn't the number of children they produce. The arrangements of the earlier eras will be modified again. If you try to pick a Golden Age and fix the rules there, well, you might as well try to hold back the sea.
So what does it come down to? Let adults enter into the kind of contracts they want within broad restrictions. Let the Churches approve or forbid whatever they want for those who put themselves under that Church's authority. And don't even try to figure out the intricate idiocies of human sexuality. People will always make their own mistakes on that score.
