For the 2nd paragraph: People are arguing over the definition of marriage as a concept. Marriage has already been established as a union between a man and a woman- people are arguing to change that definition. If the definition of the concept of marriage was a union between any 2 people, there would be no argument. Again, if there was no pre-established definition of marriage, there would be no argument! The fact is, people are trying to change the concept of marriage.
But dont you think the concept should be open to interpretation as we move forward in society with regards to equality with this issue. Thats whats happening now. over the "concept of marriage" The word concept can have many definitions also. Definitions of words do evolve over time. It could mean an abstract or general idea inferred or derived from specific instances. Or, familiarly, something conceived in the mind, as in a thought or notion, especially when it concerns generalization from particular instances. Maybe, a general notion around which ideas are developed.
I beleive the main reason many people are motivated to vote to retain the definition of marriage is the underlying idea that it represents a specific (normal) relationship. You could say thats a "nice" distinction. And I mean that in the original sense of the word nice illustrateing the problem of supposed fidelity to language.
http://www.etymonline.com/index.php?term=nice
'nice' originally meant silly, or foolish. It derived from the lation nescius, ignorant. It took on the meaning of "timid," and evolved into fastidious, or fussy. From there, it came to mean precise, or careful. It ultimately ended up with its present definition of "thoughtful," or "agreeable."
Now, you may inveigh against the dilution of the meaning of 'nice,' and insist it return to its thirteenth century meaning. But in my view, you'd be foolish (nice, eh?) to do that, because the natural conclusion is that you want us to be speaking Old English.
The absurdity of that question highlights in sharp relief the inescapable fact that language evolves. It's a natural consequence of language.
On the other hand, we should correctly resist any language change that robs us of an ability to make a useful or material distinction.
So it seem to me that if we insist that "marriage" should be retained to identify a male-female pairng, we must identify why, specifically, this identification is of value to us.