But note that most commenters there accept discounting based on risk, uncertainty, opportunity cost, etc. - which are exactly the grounds that most ordinary people, even in this very Hacker News page where you would think people would understand & accept things like expected value or probabilistic reasoning, claim to ignore the future based on.
A lot of those bases break down completely when you're talking about these time scales. Consider opportunity cost. It is not sensible to spend $50 to save $100 20 years in the future, because even at a fairly low rate of return the opportunity cost of that $50 now is over $100 in 20 years. Note that such thinking is unavoidably rooted in the idea that there will be a consistent rate of return over the period in question. That assumption isn't necessarily true if you're talking about the possibility of present decisions increasing the risk of wiping out humanity in the future.
If a similar pattern holds true, then the opportunity cost, in absolute terms, of a decision that results in fewer future humans is absolutely staggering.
