It's less about occupation, or even collective punishment against Horde races, and more about seeing that Lor'theron, Sylvannas and Gallywix meet justice for the crimes they clearly perpetrated and were complicit in. Again, ignorance is not a defence but may give Lor'themar some bargaining chips if he can be seen to be delivering justice again Aethas and other Sunreavers, but Sylvannas and Gallywix have nothing.