Of course, no one has yet discussed the moral implications of “killing” zombies, should a zombie attack be imminent.
For a handy primer, see Jimmy Akins “Theology of the Living Dead”:
http://www.jimmyakin.org/2005/08/theology_of_the.html
That’s because there are no “moral implications.” They’re dead. They need to lie still, not talk and not attempt to operate heavy machinery.