Let's take your arguement:
Currently, it is against the law in to barrel down a city street at 160 miles per hour. Why? Because you are quite likely going to kill someone. Our morals say that it is wrong to kill an innocent by-stander, therefore, society has made it illegal. What you are arguing is that, if some punk says, "I don't care if I kill someone - it ain't part of MY values." that he has the right to do it.
YOU might think that marriage is just a piece of paper. I don't, and billions of people around the world believe it is more than that, particularly Catholics (and a few other religions) who believe that it is a lifelong commitment that you cannot walk away from, and that is ordained and blessed by God, and is a profound institution that has lasted as far back as history has ever been recorded.
If, as it has been established in this thread, the relevant CIVIL rights traditionally connected with marriage can be provided through some means, without offending half the world by simply calling it something other than marriage, go right ahead. But please call it something else.
Words have deep meaning, especially when there is a long history attached to them. There is no human institution known to man older than that of marriage. As it is, I feel it is a stretch to say that civil weddings actually make a marriage. But OK, I can live with that, as it is essentially the same thing (without the moral commitment however). But having my own marriage with my wife, and our children, equated in every way, including verbally, to a same-sex partnership, I find that offensive. And I am not alone in this.
Why whould you want to offend half the world when all you need to do to avoid doing so is change the name?
The only thing you should feel when shooting a terrorist: Recoil.