...I have personally observed what look like harmful modes of thinking specific to existential risks. The Spanish flu of 1918 killed 25-50 million people. World War II killed 60 million people; 10^7 is the order of the largest catastrophes in humanity's written history. Substantially larger numbers, such a 500 million deaths, and especially qualitatively different scenarios such as the extinction of the entire human species, seem to trigger a different mode of thinking - enter into a "separate magisterium." People who would never dream of hurting a child hear of an existential risks, and say, "Well, maybe the human species doesn't really deserve to survive."
The phrase "Extinction of humanity," as words on paper, appears in fictional novels or is discussed in philosophy books - it belongs to a different context compared to the Spanish flu. We evaluate descriptions of events, not extensions of event. The cliche phrase end of the world invokes the magisterium of myth and dream, of prophesy and apocalypse, of novels and movies. The challenge of existential risk to rationality is that, the catastrophes being so huge, people snap into a different mode of thinking. Human deaths are suddenly no longer bad, and detailed predictions suddenly no longer require any expertise, and whether the story is told with a happy ending or a sad ending is a matter of personal taste in stories.
Yet I find no logic implicit in the thinking of those who are horrified at the starvation of a
comparatively few people in a faraway country... but who are positively gleeful with the thought that 1 million or 10 million times that many lives will never be lived that might be lived.
...Why does Kingsley Davis (one of the world's great demographers) respond to the U.S. population growth during the 1960s with, "I have never been able to get anyone to tell me why we needed those [additional] 23 million"? And Paul Ehrlich: "I can't think of any reason for having more than one hundred fifty million people [in the U.S.], and no one has ever raised one to me." By 1991 he and Anne Ehrlich had even lowered the ceiling: "No sensible reason has ever been given for having more than 135 million people."
If Davis or Ehrlich were to ask those 23 million Americans born between 1960 and 1970 whether it was a good thing that they were born, many of them would be able to think of a good reason or two. Some of them might also be so unkind as to add, "Yes, it's true that you gentlemen do not personally need any of us for your own welfare. But then, do you think that we have greater need of you?"
Frankly, if anything is absurd, it is the view that all else equal, the existence of one more person isn't very good. So why does this absurdity have so much appeal?