Maybe.
You are making very good arguments. I believe that the harm to society by allowing oral testimony from an interested party to estabish clear and convincing evidence of intent is much greater than any harm which can befall Mrs. Schiavo, so, in this case, I would not allow her feeding tube to be discontinued by proxy.
(Given that answer, it's probably then useless for me to point out that Michael was not the only one giving sworn testimony as to Terri's wishes -- that two others testified similarly under oath.)
I can appreciate your feelings about the people who want to uphold Terri's wishes.
But understand that I, too, fear people like you who wish to impose their religious beliefs/standards/morals/philosophy over my expressed desire not to live in such a condition.
That you would burden my spouse, my parents, and my children, both financially and emotionally, with my care is reprehensible.