I discuss a second mistake in the moral mathematics of existential risk: neglecting background risk. I show how a leading discussion of biorisk makes this mistake, and also makes the mistake discussed in Part 1 of this series.
In this post, I look at some ways in which examples are systematically misused in discussions by effective altruists. I focus on two cases: Aum Shinrikyo and the Biological Weapons Convention.
I apply lessons learned about the value of existential risk mitigation to assess the cost-effectiveness of biosecurity. Leading cost-effectiveness estimates turn out to be overstated by several orders of magnitude because they do not appropriately model background risk.