What seperates people and animals?
What makes a person a person?
What really makes us humans seperated from the rest of the animal kingdom are our cognitive abilities(this includes the fact that humans create "culture"). Anyways without our cognitive abilities we are no longer a person... we probably wouldn't even qaulify as an animal in that state, hence we call it a vegitative state. I aggree that if there is no chance of mental recovery that one should just die... unless otherwise specified by the person themselves, or if there is some chance of recovery.
