That's exactly the point being made. There are hundreds of thousands of mentally handicapped people who cannot eat, drink, go to the bathroom, change their clothes without someone doing it for them. Mentally they are considered vegetables, there is absolutely no thought process or ability to communicate.
Looking at those videos of Terri I saw a responsive person, if only minimally. So the question is: if it's ok for this woman should families of the mentally retarded be allowed to starve them as well?
I don't know the answer, but I think it bears considering, individually, if nothing else. There seems to be no mention of such problems in the Bible. That the Bible is silent on this is interesting. Did people like that not exist then?