Because if you try to impose your will on a porcupine or like-minded creature (a.k.a. whatever's in my profile picture), it will injure you. Similarly, if the government or other individuals try to impose their wills on libertarian individuals, they will defend themselves. read more
The Porcupine's origin is in the Free State Project (political migration, founded in 2001, to recruit at least 20,000 libertarians to move to a single low-population state in order to make the state a stronghold for libertarian ideas). The porcupine is the animal on their flag, which is a modified Gadsden flag. read more
The Statue of Liberty is the official symbol of the Libertarian Party, but the porcupine is used to represent libertarianism because it is a defensive animal that doesn't harm anyone who leaves it alone. For this reason, many libertarian groups and publications, including the Free State Project, use the porcupine for a mascot. read more