People should be permitted to make living wills. However, husbands should not be permitted to murder their wives with the help of Judges. Terri Schiavo had no living will. There was nothing in writing about her wishes.
Again, the covenant of marriage is not sufficient for you. Two covenants are required. You don't think that undermines marriage?
My wife and I have talked about what we want if we were ever in Terri's position, but even if we hadn't marraige means enough to me that she should have the authority to make the decision of whether or not to pull the tube.