*sigh* I just finished a skating session and am so sore I can't get into a comfy position, so I won't go into everything I'd like. Furthermore, I'm going to speak on this objectively without giving my opinion because I'm sure I'd be crucified no matter which side I was really on.
I think the root problem is not about the definitions, but rather the
root of the definition. If I'm correct (and if I'm not, someone please interject), the act of marriage has a religious base--it is two people of the opposite sex coming together in the
eyes of God. It's not so much the opposite sex part that is the problem, but Who is blessing it, IMO--that is, because of the root of the tradition, it is implied that God is okay with it. So if one sees homosexuality as an "abomination in the eyes of God" (as nate so eloquently put it

), well there'd be a problem. Religious peoples, just like everyone else, can be a bit possessive. If what belongs to the church is being given to those the church believes go against God, yes they'll raise hell about it. (Yes, one could argue this is also a problem when atheists partake in "marriage" but, for the sake of argument, let's continue not caring about that.) This is why "civil unions" started off as a good idea. It goes back to the old "separate but equal"...I think the whole point of that was to give everyone legal equality while simultaneously keeping the Church happy by separating it from what it does not approve of. Separation of church and state is what everyone wanted, right? Well, we remember how well "separate but equal" worked out the first time (not making this about race, just an example). When civil unions proved not to give equal rights to those it was designed for, we hit another problem. So we have some saying they shouldn't be equal at all, some saying it should, and some saying "If it's equal, why not just make it marriage since God loves everyone." Oh, and those who don't care, but they are not the focus right now.
This leaves the following questions to be answered: Does marriage really belong to the Church and, if so, does it retain the right to give marriage to whom it chooses? Or, since marriage now has legal ties, can the government give it to whom it chooses? Does the GBLT community just want the equal rights or must the title of "marriage" come with the package? I don't know anyone who dreams about the day they get to be "civilly unified," but if legitimately equal rights are established, they might not care.
Some of these may have already been answered--I won't pretend I've read all 7 pages of this. I'll leave you to discuss anyway.