"I don't know, therefore Goddidit" seems a cop-out to me. Even if you assume goddiddit, god did everything else, yeah? And once we understood how he did the other things, we were able to use them to better our own lives. Why would these other things that "goddid" be any different or more supernatural than previous "goddiddit" things?
Also, BlindKitty, that's all well and good, but that's your own personal theology, [even if you follow the pope, it's still your choice to follow the pope] and thus no one else should be held by the same standards unless they themselves hold those standards.
Even other Catholics, nominally supposed to agree with you, disagree about homosexuality being a sin (admittedly a small minority). Thus, legislating against it says that your ideals are more important than everyone elses. Especially about something that, according to you and yours, is a theological crime and not an actual physical crime with repercussions in the real world, like pedophilia has on the young. (Hello, informed consent!) No one is asking *you* to engage in homosexuality. And while the majorities in some (some could say most, even, but I think that's changing) countries agree with you, that's no reason to allow them to attack the minorities they disagree with. Considering the repercussions on couples that constraining marriage gives, such as one not being able to visit their partner in the hospital, not being able to file taxes jointly (monetary cost), not having your relationship automatically count for inheritance purposes, the psychological affect of your partnership being considered "less than" or "not important"... I think the anti-marriage side of "It's icky," or "It's wrong," or "It goes against my god," are nothing in the face of the actual real-world affects of constrained marriage rights, not to mention all the OTHER rights besides just marriage rights. Slavery was agreed with by the majorities in many countries for quite a long period of time, that didn't make it any less an affront against basic human decency and autonomy.
I should clarify that I don't think there's an objective morality, imposed upon us by some outside force. Especially since if you go by the Biblical morality, quite a lot of it goes against our own (modern) morality. If it were objectively true, we should agree with it, no? Just the fact that there are things in there that we disagree with, sometimes vehemently (genocide and forced abortions) and sometimes just in a head-scratchy way (not mixing fabrics, or not eating shellfish) should point to the face that we have an internal morality that we use to interpret moral teachings, like those in the bible, both New and Old Testament. Personally, I think we have a sort of basic evolved morality, created by the circumstances of our tribal and social nature. Complete with the weaknesses inherent to that (such as viewing people not of the tribe as less-than-human, and thus free to be killed or enslaved). Things like "not killing" would be that basic morality. That inherent morality is tempered by outside forces, such as religion or philosophy or experimental/external findings (such as the environmental movement gaining ground after the pictures of Earth taken from space became wide spread, the "Blue Marble", showing our fragility) Therefore, I don't believe anyone has a monopoly on moral law or teachings, and thus no one is in any position to impose their views on homosexuality or such on the rest of the population, unless they can prove an actual, physical repercussion of allowing it that disallowing it would solve. That doesn't mean I think that you can do anything you want, or the other strawmen of "cultural relativism" that would have us turn a blind eye to forced child brides, genital mutilation, or misogyny. As I said, those have actual, physical repercussions in the real world, and thus I don't believe are particularly open to interpretation of "Are they wrong or aren't they...?" It means that we must work to convince others, instead of force others, to agree with us, or at least agree to leave us be.
Goddamn that spoiler is long. I kind of got away from myself, and even then, I don't think I articulated myself all that well, or hit on all the points I wanted to. This is basically two different things in this post, only barely tangentially related to each other, hence why I separated via spoiler. Feel free to respond to one, the other, both, or neither.