So, I really think its presence under any name (marriage, union, partnership, etc.) is dangerous to the very culture. I would seek to prevent it in any form.
I understand your concern. But I would also say that one of the cultural battlefields is the war over terminology, legalism and their applications. To discriminate carefully between rights and privileges, therefore, is a clear starting point and only good can flow from it. That's why evil always tries to blur the line between the two.
But when the going gets tough, the tough get precise. And in this case, marriage needs to be connected to the church it comes from to expose what it is claiming to be when it claims to be equal. The way to do that is to rip it out of the government's authority to define it and the way to do that, is to stand on the truth of it being a right, and not a privilege, so they government cannot claim authority over it.
You would not accept the legitimacy of a Hindu or Buddhist marriage for yourself or your family members, right? But you are not threatened by those faiths using the term "marriage" even though you personally don't acknowledge their legitimacy before your faith. That's because they say they are "Buddhist marriages" and "Hindu marriages." Well, apply the same things to gays. Make them have to say, "Church of the Stunning Rainbow marriages."
Puts things immediately in perspective, and clearly points out that you do not mean, by "marriage," what they do. That's WHY blurring that definition by limiting the word merely to "marriage" through government decree is the plan of the Left.
By what authority will people be able to take the word "marriage" out of the government's dictionary?