Call it what you like. but I've never heard of a person whose actual preference was to be dehydrated to death slowly. Those who wish to be dispatched when their physical and/or mental condition reaches a certain point, want a lethal injection or other quick and guaranteed-painless means. It's appalling to me that legislators and courts are willing to authorize death-by-dehydration, but will not authorize death-by-injection. They're willing to say that in some cases it's appropriate to make a decision to stop keeping someone alive (which I happen to agree with), but then don't have the decency to see to it that it's done in a way which eliminates the possibility of any suffering on the part of the dying person, and minimizes the anguish of relatives of friends. Death is guaranteed either way -- why pretend that there's some ethical superiority to standing by passively and ensuring that it happens slowly?
If you take a terminally ill and apparently unconscious pet to the vet, having made the decision that it's life is no longer worth living, the vet does not have the legal option to just leave the animal lying in a cage without IV hydration/nutrition and just wait a few days until it dries up and dies. So why does anyone think it's okay to do that with people?