Sorry for joining so late - I’m sure I wasn’t missed - but this is one of my pet subjects and I have taken part in earlier debate on this. So here is my view:
Gay people have in my view a moral right to pursue marriage or a real equivalent.
I understand some of the legal implications BB pointed out - the only part in his argument (and that of many others) I don’t get is: How does gay marriage open the door for polyamory, incest, pedophilia, necrophilia (!) and sodomy? These activities (except for perhaps polyamory) are all declared illegal - so in order to overcome the marriage ban, they would have to overcome being forbidden in the first place. Homosexuality is legal and is therefore in a different league. So I would not be too worried of opening this door. But, hell, yes, why not create a proper civil union (same rights, same restrictions), that would do the trick. And btw open up a whole new market for divorce lawyers… 
For all the “moral” arguments against it: I think they are mostly crap … err … wrong. Homosexual behaviour is part of nature (humans do it, other animals do it) and it is in my view irrelevant if we like it or not - it will be always there and we have to deal with it. We can do this the humane way by letting people live their lives as accepted members of society, or we can make it hard on them and try to pursue, repress, therapy or baptise it away - with exactly the same result: We would still have homosexual behaviour - just many more unhappy people. Now let me think what I would choose…
Makkun