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Both are cases of a special kind of evil.
It's not really how people think nowadays, but until WWII I think people accepted wartime decisions as wartime decisions - locking up the instigators of WWII for instigating a war was pretty new territory. Penalising Germany as a state for starting WWI was, in legal terms, pretty new ground as well. Before that it was just raison d'état and the victor's spoils.
Edit to add - okay, people were locked up for starting wars previously, but more as a matter of neutralising them than as some overarching legal principle.
Both are cases of a special kind of evil. It's possible to argue that Thatcher is showing some kind of inconsistency by viewing and acting on the two remarkable cases differently. Personally I'm not sure, but it would take a whole lot of digging in to some pretty murky stuff to come to a well founded conclusion.