Now the man who seizes another’s property is living in basic contradiction to his own nature as a man. For we have seen that man can only live and prosper by his own production and exchange of products. The aggressor, on the other hand, is not a producer at all but a predator; he lives parasitically off the labor and product of others. Hence, instead of living in accordance with the nature of man, the aggressor is a parasite who feeds unilaterally by exploiting the labor and energy of other men.

- Murray Rothbard