In criminal law, juries are instructed to find a defendant not guilty as long as his or her guilt cannot be proven "beyond a reasonable doubt." The concept of "reasonable doubt" can be usefully extended by analogy to other situations, such as the argument for removing Terri Schiavo's feeding tube according to her husband's wishes but against her parents' wishes (where Terri's own wishes cannot be known for a certainty).
I challenge you to read this post and this one from the marvelous medical blog CodeBlueBlog, and all the comments to both posts, and not conclude that there is reasonable doubt in Terri's case about a) the nature, extent, and cause of her brain damage, b) her degree of awareness, c) her chances for improvement with therapy, and d) her husband's motives. I am not saying one or the other side can be proven right on any of these issues -- I'm saying there is reasonable doubt, and I have to agree with Dr. Boyle of CodeBlue (not an ideological right-to-lifer, just an ethical physician) that it is therefore morally right to err on the side of life. (The legal and federalism issues are another kettle of fish.) Boyle turns the very arguments of the let-Terri-die advocates against them (though a commenter rightly takes him to task for monolithically equating "Democrats" with that camp, since Sen. Tom Harkin helped craft the compromise bill Congress passed):
[B]y the Democrat's own argument Terri has no comprehension about what is happening, or whether or not her wishes are being fulfilled. Terri will experience nothing adverse, physically or mentally, as a result of letting her live and letting her loving parents take care of her as they wish.
As I wrote here and found suprising philosophical and bioethical support for here, I can't emotionally comprehend why Terri's parents, who gave her life, can't simply be allowed to devote themselves to sustaining her life. To me, it's more about them -- and what they, and Terri through them, may accomplish spiritually through suffering and devotion, which some call delusion -- than it is about her.