From the comments, Jane Galt asks:
…doesn’t a zero discount rate imply that even something that imposes trivial costs on each future generation should be avoided at catastrophic cost to us?
I would pose the question more broadly. If a policy imposes a great cost on one person, but involves many small benefits for others, should we always evaluate that policy by summing the respective costs and benefits and finding the net value?
The same question can be posed in both intertemporal and atemporal contexts. Philosopher Alastair Norcross made his name by considering Parfit-like conundrums. Let one person die a terrible and tortured death, but alleviate the headaches of billions of others by one second. (No, by its construction, this is not an exercise in risk reduction or Rawlsian reasoning. It is just a brute comparison of certain costs and benefits.) If the billions are large enough in number, is this worth it? Or does the suffering of the lone individual hold special status?
If we are willing to swallow this trade-off, we can accept it in the intergenerational comparison as well. I would myself balk at the notion, citing a mushy mish-mash of philosophic pluralism, quasi-lexical values, and the conceit of my moral intuitions. My conclusion is that we should modify cost-benefit analysis for (among other things) distributional concerns, but that the cost-benefit analysis should itself be done straight up. In any case, a non-zero discount rate, applied to consumption streams, would not do justice to the relevant moral intuitions about distribution. We might wish to count the wealthy for less, but not everyone in the future will be so wealthy, especially when China, India, and Bangladesh matter for the issue at hand.
Addendum: Here is commentary from Jonathan Adler.