I understand this apparently altruistic reason: rather than educate people to avoid massacres, you'd replace everyone with mannequins. So they're free to massacre mannequins. If we are to become saints because we made synthetic goo to save cows, I'd say we are still pretty lazy because we learned nothing about the ethics of killing other suffering beings like us on this planet. (Being provocative: of course there is already empathy in that reasoning, but the root cause is still out there; our lack of empathy and greed.)