iO9.com recently posed the question "When is it okay to kill zombies?"
To answer the question, one must balance threat, the value of human life and the concept of infected vs. undead zombies.
First, she speaks with David Daigle of the CDC, who helped craft their own preparedness guide, and who says killing zombies are never recommended, and that quarantine is preferred. Then she consults Kyle Munkittrick of Pop Bioethics, who suggests that a zombie infection that turns people into Night of the Living Dead or Walking Dead undead shells of themselves is actually a mockery of human dignity. But even if the zombies are simply infected by a 28 Days Later-type rage virus, killing them may be an imperative. He further discusses the need for survivors to have an end-of-life conversation about how they'd prefer to be dealt with once infected. Davis finally asks when we should consider zombies to be a separate species unto themselves, with a right to survive.
It's fascinating stuff. Check it out.