Maybe he should stick to his science or read some more because that is not how society works or worked at all. What is humanity's biggest strength but working (and thinking) together? Can in this regard a "old sick cripple" not be just as valuable as a healthy young person? Indeed they can and have been countless times. Pretty much nothing we have could be had without thousands of people working hand in hand, even if they never meet.

Natural selection is not very much a thing for us. I would rather call it societal selection, as we decide what is valuable and what is not. Who gets to live and who gets to die. And these decisions are shaped in most parts by our very much chosen modes of economy.