A virtuous person happily confers justified benefits and unhappily bestows even justified harms. Moreover, it is not just that the virtuous person is happy about someone being benefitted and unhappy about someone being harmed, though she does have those attitudes. Rather, the virtuous person is happy to be the conferrer of justified benefits and unhappy to be the bestower even of justified harms. These attitudes on the part of the virtuous person are evidence that it is non-instrumentally good for one to confer justified benefits and non-instrumentally bad for one to bestow even justified harms. Of course, the bestowal of justified harms can be virtuous, and virtuous action is non-instrumentally good for one. But an action can be good for one qua virtuous and bad for one in another way—cases of self-sacrifice are like that. Virtuously bestowing justified harms is a case of self-sacrifice on the part of the virtuous agent.
When multiple agents are necessary and voluntary causes of a single harm, the total bad of being a bestower of harm is not significantly diluted between the agents. Each agent non-instrumentally suffers from the total bad of bestowing harm, though the contingent psychological effects may—but need not—be diluted. (A thought experiment: One person hits a criminal in an instance of morally justified and legally sentenced corporal punishment while the other holds down the punishee. Both agents are equally responsible. It makes no difference to the badness of being the imposer of corporal punishment if instead of the other holding down the punishee, the punishee is simply tied down. Interestingly, one may have a different intuition on the other side—it might seem worse to hold down the punishee to be hit by a robot than by a person. But that’s a mistake.)
If this is right, then we have a non-instrumental reason to reduce the number of people involved in the justified imposition of a harm, though in particular cases there may also be reasons, instrumental and otherwise, to increase the number of people involved (e.g., a larger number of people involved in punishing may better convey societal disapprovat).
This in turn gives a non-instrumental reason to develop autonomous fighting robots for the military, since the use of such robots decreases the number of people who are non-instrumentally (as well as psychologically) harmed by killing. Of course, there are obvious serious practical problems there.