PRINCETON — Of all the arguments against voluntary euthanasia, the most influential is the "slippery slope": once we allow doctors to kill patients, we will not be able to limit the killing to those who want to die.

There is no evidence for this claim, even after many years of legal physician-assisted suicide or voluntary euthanasia in the Netherlands, Belgium, Luxembourg, Switzerland and Oregon. But recent revelations about what took place in a New Orleans hospital after Hurricane Katrina point to a genuine danger from a different source.

When New Orleans was flooded in August 2005, the rising water cut off Memorial Medical Center, a community hospital that was holding more than 200 patients. Three days after the hurricane hit, the hospital had no electricity, the water supply had failed and toilets could no longer be flushed. Some patients who were dependent on ventilators died.