Full Idea
Rejection of the doctrine of double effect puts us hopelessly in the power of bad men. Anyone who wants us to do something we think is wrong has only to threaten that otherwise he himself will do something we think worse.
Gist of Idea
Without double effect, bad men can make us do evil by threatening something worse
Source
Philippa Foot (Abortion and the Doctrine of Double Effect [1967], p.25)
Book Reference
Foot,Philippa: 'Virtues and Vices' [Blackwell 1981], p.25
A Reaction
Her example is they will torture five if you don't torture one. Bernard Williams's famous Jim and the Indians is they will shoot twenty if you don't shoot one. Williams aims it at utilitarian calculations. Double effect is highly relevant.