The purpose of sneering about "idiots" and inventing pseudoscientific gibberish about natural selection is to wash one's hands of moral responsibility for scamming naive young people, the elderly, or adults with psychiatric or cognitive disabilities. "It wasn't me robbing your college-age son out of a new car, that was just natural selection doing its thing! So long, losers!"

My mom was a very crappy person who strongly believed in the "sucker born every minute, separate a fool from his money" mantra. I think it's become a core American ideology.