Firstly, the so-called Islamic State has been in charge of Mosul for eight months. It was the capture of the region that prompted the unilateral renaming of the rebel organization as a 'state'. So these ISIL heroes with sledghammers were attacking property of their own organisation, not the displaced Iraqi government.
The second issue one might have with the lobbyist's argument is that it ignores the actual reason for the actions we are discussing. Just as in the US, fundamentalists are trashing artefacts in search of pieces of text to legitimise their crusade, so similar motives lien behind the actions of the wahhabists and salafists. Christopher Jones has an article on this in Hyperallergic ('What ISIS Destroys, Why, and Why We Must Document It', March 6, 2015). The dealers and collectors of "ancient art" might do well to reflect on what it means for them. In particular, I would draw attention to the end of the video where there is shown a photograph of the excavation of one of the lamassu from Nimrud with a caption stating that
“These idols and statues were not visible in the days of the Prophet Muhammad and his companions, but were extracted by the worshippers of devils.”What does that make of the collectors of ancient art and the collectors of coins with images on them?
Vignette: "Ancient discs with devilish images for titillation of kuffar".
UPDATE 9th March 2015:
Another one that went wa-a-a-y above the head of blinkered coineys. "it is only ritual abduction" argues Dealer Dave, wrapped up in his tiny world of self-justification. Tell that to the fundamentalists when they come for you.