This debate could go on forever without either side being satisfied with an answer. De Wallen, you brirng up excellent points regarding same sex relationships, and relationships in general, and from a purely academic standpoint, it is even possible that the reasons for same sex marriage outweigh the reasons against it.
The only true reason that I could state to support the viewpoint that it is wrong, would be that according to the doctrines of my church it is wrong. I hear academic reasons supporting same sex marriage on an almost daily basis (due to the large homosexual population where I live) and they make sense in my mind...but I learned long ago to trust in my faith instead of my mind when the doctrines of the church are at issue. I have been called a "sheep" and worse for this, but that is my reason for believeing what I believe.
I understand if this reasoning doesn't sit well with you, and I hope that you understand that the position of the church regarding same sex marriage is not an attack personally on homosexuals, and that the church welcomes all people who are actively seeking the truth, with pure intent.