If two individuals enter into a contract to commit trespass, theft, robbery or murder upon a third, the contract is unlawful and void, simply because it is a contract to violate natural justice, or men's natural rights.
The Complete Works of Lysander Spooner: The Unconstitutionality of Slavery, No Treason: The Constitution of No Authority, Vices are Not Crimes, Natural ... Laws of Congress, Prohibiting Private Mails