The only problem with what you say is that what is being done to Teri Schiavo has been routinely done for at least a decade. The only real difference is that part of her family opposes it and has succeeded in turning it into a media firestorm.
Absent clear and irrefutable proof of an individual's wishes (which is the case here, and I don't know how many other times, but whatever they are doesn't attest to the rightness or wrongness of the act), deciding on their behalf that they should die places our moral souls in mortal peril. Once you establish that principle as being morally acceptable, and once you choose death as being preferable to life, you open the door to unspeakable atrocities, all perpetrated in the name of "what's best".