The question in the extant case was not whether anyone had the obligation to feed Terri, but whether anyone had the right to forbid Terri from being fed.
During medieal times, families with unwanted children would abandon them by the side of the road. They might starve, get eaten by wild animals, or be rescued. Even though the odds of the children getting rescued may not have been very good, the parents who left them by the side of the road at least gave them something of a chance.
Terri Schiavo had parents who were willing to care for her at their own expense (with the aid of many who offered their help of their own free will). Even if nobody had an obligation to care for her, why would that imply that those who wanted to care for her should be unable to do so?
No. The actual question in the case was whether or not Terri Schiavo was able to eat on her own, and whether or not she could swallow that food. She could not.
Her parents, hoping against hope, found "doctors" who fed into their unrealist hope.
I ask you the question again:
If a person, even Terri Schiavo, could NOT chew, eat or swallow, and they have NO HOPE of getting better, isn't a feeding tube unrealistic, unnatural, and an attempt to circumvent God's purpose for that person?