The Problem of Collective Harm: A Threshold Solution

Many harms are collective: they are due to several individual actions that are as such harmless. At least in some cases, it seems impermissible to contribute to such harms, even if individual agents do not make a difference. The Problem of Collective Harm is the challenge of explaining why. I argue that, if the action is to be permissible, the probability of making a difference to harm must be small enough. This in turn means that both the probability of harm and the probability of avoiding harm have to remain below the corresponding threshold probabilities. I compare this threshold probability account to proposals that revolve around difference-making, NESS causation and security dependence, and I argue that they fail for reasons of scope. For instance, a moral principle that invokes NESS causation prohibits so many actions that compliance with it would have a stifling effect on human life.