In that scenario I would not know what to say either.  Perhaps I would point out that I didn't actually do anything, hence I didn't actively kill anyone.  But I agree, it's tricky.  But if I did steer for a sparsely populated suburb, and the mother of a dead child asked me, "why did you decide to aim at our suburb, I lost my husband and my little child", I would not feel good about saying "If I had done nothing, five times more people would have been killed. So, I aimed at your suburb".