Think about it: The Joker is criminally insane. He's killed before, and he will kill again. If he gets locked up in Arkham, he'll eventually escape again. So killing him will save lives.
In fact, would refraining from killing him when the opportunity arises be an ethically blameworthy act of...
More: http://www.psmag.com/health-and-behavior/can-an-animal-have-rights-and-still-be-dinner (August 19, 2015)
It seems the only way the author can answer "yes" to this question is if it's meat from animals that have died not by the deliberate hand of humans. Is that still ethically acceptable?