In the beginning of Avengers: Age of Ultron (see clip), Strucker's Hydra base is raided by the Avengers, but it looks like the Avengers try to stun, not kill. It's especially highlighted when Iron Man tries to talk down a group of soldiers, but they keep shooting, so he shoots them and says "It was a good talk", to which one of them replies "No, it wasn't!". Nevertheless, literally one second later Iron Man shoots Dr. List to death even though Dr. List posed no physical threat. Strucker himself is soon taken alive by Captain America.
So why was was Dr. List treated differently? Is it because Dr. List tried to delete files that for Iron Man are worth killing over? Or because Iron Man decided List deserved death for sort of being a torturous doctor like Josef Mengele? In that case, would Iron Man have killed List's superior Strucker too had he gotten to him before Captain America did?