Ah, I see.
I think that marriage is a bond between man and women just by definition of it. So I see at least one reason to ban marriage between gay people.
Call it differently, I (and many others) will have no reason to oppose. Like, for example, civil union. E.g., marriage assumes civil union, but civil union can be between gay people, triples, teams of eight and so on.
As there is mostly heterosexual couples in the world, I think we have very valid reason to call this very common case of civil union by using special term. Let's use the term marriage. I think that provides you with the reason to stick with this term for this specific case and other terms for other cases.
Government discriminates people from top to bottom for various reasons, from age to the gender, to the wealth to the height. I do not see the reason to discriminate gay people in their discrimination by government.