The reason is that very soon the baby boomer generation is going to stop being productive, and start being a cost on society as their health care needs multiply. In order to save money, killing the patient must become a morally equivalent option to treating them. Which "treatment option" they recieve will be based on a cost/benefit analysis to society.
And then we can all be GODS in our own eyes.
Not to big of a leap from deciding when to abort the most innocent who has no input in the decision. See we are well on the path to being/playing GOd.