The morality of discounting

There’s a showdown at Overcoming Bias between Eliezer and Robin over discount rates. Eliezer says,

I’ve never been a fan of the notion that we should (normatively) have a discount rate in our pure preferences – as opposed to a pseudo-discount rate arising from monetary inflation, or from opportunity costs of other investments… If you wouldn’t burn alive 1,226,786,652 people today to save Giordano Bruno from the stake in 1600, then clearly, you do not have a 5%-per-year temporal discount rate in your pure preferences.

While this is music to the ears of environmentalists everywhere, Robin replies,

Very distant future times are ridiculously easy to help via investment. A 2% annual return adds up to a googol (10^100) return over 12,000 years, even if there is only a 1/1000 chance they will exist or receive it.

So if you are not incredibly eager to invest this way to help them, how can you claim to care the tiniest bit about them? How can you think anyone on Earth so cares? And if no one cares the tiniest bit, how can you say it is “moral” to care about them[?]

I don’t have a fully formed opinion on this, but I will raise two issues that occur to me when I read the debate. First, loss aversion: the loss of a billion lives is not the opposite of helping a billion people in one’s mind. The loss of life figures far greater, so it’s not a fair comparison to make.

Secondly, there is a big difference between the way people should discount (Eliezer) and the way people actually discount (Robin). I doubt people have identical discount rates, either across people or even across objects for a single person. Even if they did, would we want to make decisions based on peoples’ individual preferences? Individually we may not be willing to sacrifice much to help future generations, but does that mean that we agree that there is no moral imperative to do so? I may not be willing to shoot one innocent person now in order to save 1 billion in 400 years, but I may still agree that it should be done.