The Knobe effect is that people judge cases of good and bad foreseen effects differently with respect to intention: in cases of bad effects, they tend to attribute intention, but not so in cases of good effects.
Now, this is clearly a mistake about intention: there is no such asymmetry. However, I wonder if there isn’t a real asymmetry in the value of the actions. Simplify by considering actions that have exactly one unintended side-effect, which is either good or bad. My intuition says that an action’s having a foreseen bad side-effect, even when that side-effect is unintended and the action is justified by Double Effect, makes the action less valuable. But on the other hand, an action’s having a foreseen good side-effect, when that side-effect is unintended, doesn’t seem to make the action any better.
Let me try to think through this asymmetry intuition. I would be a worse person if I intended the bad side-effect. But I would be a better one if I intended the good side-effect. My not intending the good side-effect is a sign of vice in me (as is clear in the standard Knobe case, where the CEO’s indifference to the environmental benefits of his action is vicious). So not only does the presence of an unintended good side-effect not make the action better, it makes it worse. But so far there is no asymmetry: the not intending of the bad is good and the not intending of the good is bad. The presence of a good side-effect gives me an opportunity for virtue if I intend it and for vice if I fail to intend. The presence of a bad side-effect gives me an opportunity for vice if I intend it and for virtue if I fail to intend.
But maybe there still is an asymmetry. Here are two lines of thought that lead to an asymmetry. First, think about unforeseen, and even unforeseeable, effects. Let’s say that my writing this post causes an earthquake in ten years in Japan by a chaotic chain of events. I do feel that’s bad for me and bad for my action: it is unfortunate to be the cause of a bad, whether intentionally or not. But I don’t have a similar intuition on the good side. If my writing this post prevents an earthquake by a chaotic chain of events, I don’t feel like that’s good for me or my action. So perhaps that is all that is going on in my initial value asymmetry: there is a non-moral disvalue in an action whenever it unintentionally causes a bad effect, but no corresponding non-moral value when it unintentionally causes a good effect, and foresight is irrelevant. But my intuitions here are weak. Maybe there is nothing to the earthquake intuition.
Second, normally, when I perform an action that has an unintended bad side-effect, that is a defect of power in my action. I drop the bombs on the enemy headquarters, but I don’t have the power to prevent the innocents from being hit; I give my students a test, but I don’t have the power to prevent their being stressed. The action exhibits a defect of power and that makes it worse off, though not morally so. Symmetry here would say that when the action has an unintended good side-effect, then it exhibits positive power. But here exactly symmetry fails: for the power of an action qua action is exhibited precisely through its production of intended effects. The production of unintended effects does not redound to the power of the action qua action (though it may redound to its power qua event).
So, if I am right, an action is non-morally worse off, worse off as an exercise of power, for having an unintended bad effect, at least when that bad side-effect is unavoidable. What if it is avoidable, but I simply don’t care to avoid it? Then the action is morally worse off. Either way, it’s worse off. But this is asymmetric: an action isn’t better off as an exercise of power by having an unintended good effect, regardless of whether the good side-effect is avoidable or not, since power is exhibited by actions in fulfilling intentions.