Threat of sabotage as a driver of collective action

A model is presented where the welfare of contributors to a public good can increase when they face an adversary who ex post sabotages their efforts. It is a best response for the adversary to maximally sabotage the smallest effort, thus increasing a defector's marginal product of effort. This creates a kink in the individual contributor's payoff function around the equilibrium effort, which can lock contributors into exerting high effort. For a sufficiently large degree of complementarity between the contributors’ efforts, the adversary increases contributors’ welfare. This result is robust when departing from several simplifying assumptions of the model.