Suppose I am considering doing X, and doing X is a participatory cause of some sorites outcome Y. Suppose further that the sand pile in question is made of millions of grains of sand, and that in doing X I am adding one grain: that is, the end result will be a sand pile whether or not I do X (or whether or not I even exist, for that matter). I can only do X once, unless I live in Chicago.
Doing X will have two kinds of effects: effects which depend on our sand pile being larger than some other group's sand pile, and effects which will only occur if I personally do X.
Proposition: Under double-effect, if doing X has evil effects which obtain whether or not our sand pile is larger than their sand pile, I can only justify doing X on the basis of good effects which obtain whether or not our sand pile is larger than their sand pile.
That is, I am first and foremost morally responsible to justify the effects which directly flow from my own act.
(Cross-posted)