I thought that Cass Sunstein’s EconTalk podcast on worse case scenarios had an interesting discussion of discount rates (this section starts at about minute 55 and it is about 9 minutes long). He argue’s that there’s a difference between discounting lives and discounting money because money has opportunity cost; you can invest money and make it grow, whereas you cannot do the same thing with lives. that we should not have a discount rate in our pure preferences However, Robin Hanson dissented.
I tend to side side against discount rates in our pure preferences. Even if people act like they have discount rates in their pure preferences (note the lack of charities trying to help the future), as Hanson points out, perhaps they would if they understood how easy it is to help the future.