Sorry to rant, but I am going to.
What is wrong here is not in the logic of the statements you question, it is in the weird attachment a modernity shaped by Christianity has made to feminine morality in the name of a patriarchal God.
God is not against killing. Even in the most rigid version of Evangelical Christianity, there is no logic to be had in this notion. Jesus condemns wealth a dozen times as often as violence, and never mentions killing.
The early Church thought the world was ending soon, and we might all have fairly few years of life left anyway. They were much more concerned about being kind to people while they were alive.
The Old Testament is even clearer on this issue -- the first few murderers in the Bible go free, while the first rape mentioned is avenged with the deaths of an entire village.
Killing for stupid reasons is out, but the word we translate as 'kill' in the ten commandments does not apply to war, or punishment, or appropriate vengeance, and may actually not cover most of the reasons people kill. Otherwise the recounted killings to avenge rape, or punish adultery, or take Jericho would not be demanded and praised in the same text.
OK, enough ranting at people who cannot read their own books.
Our morality in the meantime has slid into what Nietzsche calls 'slave' morals, where the preservation of life is always paramount, discarding a whole host of traditional male values in the process.
Morality is obviously about more than preserving life, it is about allowing people to actually live. If that means that sometimes they only live for a shorter period, because they choose to stand up for the freedoms of people in another country; then that can constitute "really living", more than staying home and fretting about it.
We like to give people choices in modern societies, but one of those choices can be whether or not to become part of a military force and risk having to balance the value of individual lives against all the rest of the values of one's own and one's society.