Your question is not well phrased. The law allows someone to kill to defend themselves, they nevertheless still have to prove such a circumstance. Should a person be allowed to kill in self-defense? That is a personal choice.
Genocide
Murder, genocide.
The killing of people who cannot defend themselves is considered to be an act of murder or homicide, and is widely condemned as a grave violation of human rights and ethical principles. It is often seen as a cowardly and unjustifiable act of violence.
They should defend themselves.
First of all the question should be, How do chimpanzie's defend themselves?, ramrod. How the hell do you think they defend themselves? Its called putting 2 and 2 together...
Porcupines defend themselves with their quills.
They defend themselves by releasing disgusting slime when attacked.
Porcupines defend themselves with their quills.
They run away from predators or may defend themselves using their horns.
by killing people.
Just about all animals will defend themselves when that becomes the only option. But bald eagles killing humans - never heard of that happening.
Anybody could do what they wanted including taking things that do not belong to them and killing other people. People would have to defend themselves. There would be no "society".