"Under what circumstances is it moral for a group to do that which is not moral for a member of that group to do alone ?" 

― Robert A Heinlein

all of society is organised into groups so that _we_ may do in what _i_ can't or won't  do. 

think of the firing squad - why need a firing squad at all ?   one person can just walk up to the condemned, put the barrel of the gun to their head, and  pull the trigger .... 

this is not done because men can't take too much of this, and it destroy's morale; hence the firing squad. 

( in fact, this comes from the files of Eichmann  - the nazis used to do this to the jews at first, but the guns began overheating, and also, morale began to drop, so more impersonal and efficient methods needed to be found..) 

a member of the firing squad  doesn't know if he is given live bullets or not;  and whether one's shot hit the condemned or not.  hence , the firing squad reduces to a bunch of individuals, each firing what _may_be_ real ammunition, towards the condemned 

- and NOT -

"men who shoot and kill the condemned" - because this statement will not be true for each member of the squad. 

hence ,  a group can kill, while an individual does not 

the commanding officer - the one who brings the squad and condemned together, and exercises his authority in making the squad shoot on his command, is not pulling the trigger, and hence is also not 'doing the killing'

//  is this a ship of Theseus problem ? 

// is this a "I was just doing my job" problem ?

can you punish the hand for what the brain asked it to do ? but the hand is not autonomous whereas the individual is (or so we believe for now)

if you were to reverse the moral logic, and insinuate that every person in the group is guilty of killing , then by extension, you and me are also guilty of the same thing by virtue of just existing in the society that employs firing squads 

by extension, you and me are guilty for every deforestation, every bit of polluted soil and air, every death by road accident etc

on a different note - 

when matter compilers and nano assemblers become household items, do we have to carry the karma for ALL those who died before, or do we get a fresh slate ?

ultimately, every aspect of human life is being part of a 'firing squad', and we get by thanks to our addictions, be it sugar, caffeine, alcohol, or digital content. this is the human condition, of man, in society.