infanticide vs. quality of life

Is it fair for a physician to end the life of a newborn? There are many issues: first and foremost, the quality of life of the infant. Is it ok for a physician to help aid the in the death of an infant who will not survive long, if at all, after birth? Is it ethically acceptable for an infant, who would survive after intensive treatment, to be left to live. Even considering there is extreme abnormalities, brain damage or organ damage. Where do you draw the line? Or what about the infants that do not depend on any form of life support, but would suffer from incurable, untreatable diseases. Suffering, in pain, for however long they survive. What about the parents. Most parents love thier children unconditionally, that is a fact. But to see your child suffer, how do you survive? I am not saying that this is or is not an acceptable medical practice. This opens a lot of doors for questions. How does one truely distinguish if the infant's prognosis is truly death, or would the infant live out a full life? What about the infant's rights? They cannot speak up for themselves. They have obviously not yet learned to express, or feel emotions. What gives doctors the right to play the role of God?