Yes.
If you don't believe in sharing and the whole two way street, think of this.
If something happened to the one you're with and they're on life support and there was a choice to pull the plug or have them continue on life support; don't you want to be in charge of that option since you're the one that is in a relationship with them, loving them for so long?
Well if you don't get married it's entirely up to their parents & family, not to a girlfriend.
I also think marriage is a lot more then just that, people have lost the concept of marriage. Marriage is supposed to be a commitment between two people who love eachother and agree that they want to spend the rest of their lives together for better or worse. Unfortunately, people have lost the concept.. but I am not one of those people and I am currently engaged.
What's mine is his and what's his is mine, we belong together and we will spend our time together because a marriage is much more then just vow's and a name change, it's a commitment.. people just don't realize that anymore.