Time for a new perspective.
[Disclaimer: My intention is not to offend anyone, just to add a new perspective. That said, some of this could easily come across as offensive, particularly my insouciant way of talking about sensitive subjects. If you don't like what I have to say, feel free to ignore it—at the cost of your own potential ignorance. If you just don't like my tone, please forgive me and laugh. Really, I have a dry sense of humour…]
I'm a history student, so that's my specialty. I've read several books on the History of the Family, because it interests me. I love social and cultural history… anyway, enough intro.
Your discussion ignores millenia of history. Let me explain:
Marriage, for most of history (= the written past), and presumably for ALL of prehistory (which is quite a long time for those who don't believe in a young earth), was usually based on factors other than love. Often those getting married had no say at all. Often they had some say, but not absolute. On rare occasions, they could choose what they wanted. In all three of these cases, economic, reproductive, and family connections were the primary reasons for marriage. I could cite countless examples, but I hope you can take this one on faith. Love was sometimes taken into account in choosing a marriage partner. Often it was not. Even when it was, it was rarely the determining factor. There was no point in marrying for love if your children would starve to death (how loving).
By now, you may be thinking "how cruel and oppressive those people were! How good it is we're more enlightened now!" Studying history, however, might change your mind. Marriage served a function. Roman political candidates were regularly asked about whether or not they had entered into marriage with the intention of raising children. It's hard for Americans to understand this, but who you married could make or break you and your entire family for the rest of your life. And after that it would seriously affect your children. As a rule, people married for reasons that made a lot of sense in a lot of non-emotional ways. It's important to realize, however, that a great many people fell in love during their marriage. This still frequently happens in arranged marriages.
Homosexuality has also been generally universally condemned historically. Why do you think this is, if it's clearly harmless to society? Homosexuals have just had rotten luck? People have been cruel and evil for all of history, and are suddenly enlightened now? I don't want to press this point, but I'm simply talking about universality. If you study enough, you'll start to pick out that certain behaviors are advantageous, and certain are not. Homosexuality, as a behavior, had nothing beneficial to offer over heterosexuality. That said, that's never stopped a lot of people. People still bing drink, though the benefits are scant. People still commit suicide; hardly an advantageous decision. I may sound cold, but realize that I'm only approaching this in the context of function at the moment. Love served an important function—to draw individuals closely together in a way that will make them work better together in various contexts. Sexual love was functionally significant in child-raising. Love between family and friends and "coworkers" was important for various other reasons. Some times people didn't quite get the right emotions in the right relationships, and this was maladaptive in an evolutionary sense.
"What about the Greeks?!" One may cry. Well, yes, many (though certainly not all—Plato put homosexuality in the same category as incest) Greeks praised homosexuality. Generally speaking, however, this came in the form of pederasty (other forms were much less common). So, yes, many Greeks thought homosexuality was great—generally the same Greeks who thought that having sex with children was great.
Life has changed. Marriage has taken on whole new meanings these days. The "Companionate Marriage" is common, and many feel that there should not be any distinction between concubinage and marriage and civil unions. What to do with that, I can't tell you. I'm not a sociologist. But this wasn't really an issue historically. And for some people today, it still isn't. You can have a perfectly satisfying life (if records are any sign) without making love pivotal to your life. You can get married, have children, and be happy. You can also be perfectly happy without ever drinking (though the French would never believe it). You can even be happy without ever being able to speak. Helen Keller was quite outspoken on this. Now, don't take this the wrong way; it applies to me. I really, really, really want to get married. I've been engaged for over two years, and not being willing to shack up with my fiancée or anything before we're married, this is very, very frustrating to me. I recently realized, however, that I was being stupid about it, and making myself unhappy—I was choosing to focus on my desire to be with her. You can argue that love is something I just can't control, or you can argue it isn't. I don't care. I'm deeply in love with her, and that's not going to change. But I can shift my focus. Make my relationship with her less important in comparison to, say, my writing. It's not what I want, but man, I find that by shifting my focus, my life is now both more fulfilling and much happier.
And, shockingly, some people manage to be quite happy while celibate. Hard to believe, eh? Maybe these people were born asexual. I don't know. Maybe they're just deluding themselves, or they don't realize what they're missing—but then, what kind of a bigot would judge other people's current happiness on moral grounds like that, right?
I'm not talking about causes here, or choice of orientation. I'm not interested in it. I'm not talking about psychology; that's my fiancée's specialty (seeing as she's getting her degree in Psychology in one of the most respected Psych programs in the world this May). I'm talking about history, and how we might just fit into it, or apply some of its lessons to ourselves. I'm not going to tell you if you can change how you feel about this or that person—that's your job (or a psychologist's).
From my personal perspective, I just don't see the function of homosexuality. What does it do for its practicioners? How does it give them an emotional/competetive/social/mental/spiritual/evolutionary/scientific/etc. edge?
This may seem awefully cold, but I like to think it's fairly rational. But then, I've a little experience with love, myself. I believe that, for someone with self mastery, love is ultimately a choice. You choose to love, or to stop loving someone. If you're smart, you can figure out how to never fall out of love, or how to fall in love with someone again. At the same time, you can choose to stop loving, or choose to love again. I'm not going to pretend like it's easy. It usually isn't. But choosing love is something that can, and must be, done, for (most of) those who wish to always love faithfully. This concept is arguably at the core of Christianity, but that's a whole other discussion.
So that's my 2¢. I hope it's something you haven't considered before. I have few delusions, and I certainly don't expect to change anyone's mind on anything they feel strongly about. But I hope you feel a little better informed now, and have a greater perspective on things. I really don't want to get into an argument, so if you're about to, stop. You can provide a different perspective, but I really hate arguing; an awful lot of experience has taught me that people generally don't change their minds, even (especially?) when they've been soundly thrashed in the mental arena.
Feel free to discuss whether or not people can choose to love in another thread. That's not a matter of history, and is terribly philosophical, so I figure it's fair game.