For example, consider slavery. Slavery is a system in which a nonviolent human being must labor for another under the threat of aggressive violence. For Rothbard, slavery is unjust because it violates the non-aggression principle. Therefore, slavery must be illegal. Now consider the case of drinking alcohol. Although it may be morally reprehensible and bad for one’s health, drinking alcohol
does not involve the use of violence against a nonviolent human being. Therefore, drinking alcohol must be legal. In this manner, Rothbard uses the non-aggression test to determine whether any act is just or unjust and must be legal or illegal.
Although the non-aggression principle itself has never been controversial in the history of thought, its implications can be shocking for the uninitiated. For example, consider the case of taxation. A tax is a payment that government extracts from a human being under the threat of aggressive violence. To Rothbard, taxation is unjust because it violates the non-aggression principle. Any logically consistent thinker who accepts the principle must reject taxation.
Edward W. Fuller
Rothbard A to Z, xxvii
Full article by James Corbett here: https://www.corbettreport.com/5-important-lessons-absolutely-no-one-will-learn-from-iowa/