It makes sense to me, as someone, the patient, may not have the words to be able to say they want to continue on with their life, even if others don't see it as a viable existence. If the courts, law is changed to make it permissible to end someone's life without their consent, then that could lead down the road to killing a person for the sake of the estate of that person, or just because the relatives think its the right thing to do. Don't confuse putting an animal to sleep, to save it from suffering, and a human being, they are not the same thing at all. The person who assists in the killing of another human being should be looked at by the courts, law, which should be done on a case by case basis, and it shouldn't be carte blanche to take someone's life, even if they say you can. They may be making that point whilst under duress, with a serious but treatable illness.
After reading about the effects of withdrawing food, water and medication from a patient, seems about as inhumane way to treat a human being as is possible to imagine.