My own personal view is that overwriting or dispelling a global should not be seen as breaking an NAP, but instead should be viewed as a tool for forcing your opponent to break the NAP for you. Think diplomacy and real world politics. Of course I fall more into the playing for fun camp than the playing to win camp. (Not that I dislike winning mind you.
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The whole contention over the interpretation of NAPs is the biggest reason my multiplayer games are reserved for close friends instead of the public boards. Not knocking anybody, just giving my $0.02.