This seems like a mighy weak arguement considering that they are trying to kill her anyway. Which raises a red flag. If they were smart they would allow this, that way if she did aspirate and die, they would not be held responsible for her death.
The fact that they are fighting this so badly makes me think that they are worried that she just might be able toeat on her own, even if it is soft foods or liquids at first.
Your point is indisputable and totally logical, but the people you are debating with want Terri dead as well.