"as a criminal organization with all of its income and assets derived from
the crime of taxation, the State cannot possess any just property. This
means that it cannot be unjust or immoral to fail to pay taxes to the State,
to appropriate the property of the State (which is in the hands of
aggressors), to refuse to obey State orders, or to break contracts with the
State (since it cannot be unjust to break contracts with criminals)." Ethics
of Liberty, p. 183.
http://www.mises.org/rothbard/ethics/ethics.asp