I never heard this argument before, but it's quite elegant. Hitchens points out there are four conditions under which a country loses their sovereignty.

1. Repeated aggression against other states.
2. Violation of non-proliferation treaties.
3. Harboring of gangsters or terrorists wanted by other states.
4. Committed acts of genocide.

Iraq, prior to the 2003 invasion was in violation of all four conditions. Iran, in contrast, can only be said to be in violation of #2 and #3 (and vaguely in violation of #1). North Korea can be said to be in violation of #2.