I don't know anything in the NT about Christians killing non-believers. I was talking about the statement about "having love among yourselves". JWs are the practically only ones who fulfil that since they refuse to kill each other in war. It's amazing when you think about it, nearly 10 million people spread across the earth who refuse to go to war against one another. If only everyone took the same stand.
Because if everyone acted as JWs there would be no wars and no killing. It's a basic question in ethics: "what would happen if everyone acted that way?" There would be no war to start with, that's what would happen. And the world would be a much better place.
Apart from which I think there's good evidence for the early Christians refusing to go to war just as there is good evidence about them using the divine name. So it's another aspect where JWs copy the early Christians and are reviled for it.