I’ve seen a lot of discussion by fans asking how the Doctor could just kill the Ganger Amy when the entire episode was dedicated to proving that the gangers were in fact just like people. So I figured I’d write something about how they justified this action.
The reason that the Doctor was telling the miners that they could not kill their gangers is because the gangers were at that point autonomous. The solar storm had given them their own lives. Before that, yes, they thought they were really people and they felt themselves dying when they were “decommissioned” but they still required the human version of themselves to be piloting. They could not exist while without the pilot. When the storm happened this ceased to matter.
However, the ganger version of Amy was not autonomous. It still required Amy to be hooked up to it somehow. The Doctor said he was trying to trace the signal, that was between human Amy and ganger Amy. As long as the ganger existed human Amy was unconscious. The Doctor had to kill ganger Amy because he wanted human Amy to be conscious for the birth. He also killed the ganger Amy because he could it kill quickly and painlessly rather than the procedure of “decommissioning” that the humans usually used.
He killed the ganger Amy not because he wanted to or was vindictive but because he had to and he knew he could do it humanely. You could tell it hurt him but, as is so often often the case with the Doctor’s actions, there wasn’t really a workable alternative.