The doctrine of double effect (DDE) and my suggested correlative, the doctrine of single effect (DSE), suggest that no significance should be given to either the lawful nature of the threat or the potentially beneficial side-effects of blackmail. Under DSE, the blackmailer violates deontological constraints if he threatens disclosure in an intent to obtain money or other advantage because, inter alia, were he to have alternative threats available he would threaten anyway. The nature of the threat is outside the intent of the blackmailer in the same way the killing of civilians is outside the intent of the strategic bomber. Since the blackmailer's end is harm, it is not redeemable by the possibility that some component of the means he used might be lawful. Like the terror bomber, the direct intent of the blackmailer is to do harm, and as with terror bombing, such intentional harm is impermissible regardless of its beneficial side-effects.
Wendy J. Gordon, Truth and Consequences: The Force of Blackmail's Central Case (Jan. 10, 1993) (unpublished manuscript).