If it was a mistake, it was a mistake. It happens. But on those cases where it is done on purpose, it is a deliberate show of disrespect. A slap or spit in the face when tensions are already at the boiling point. The person delivering the slap should know better, and can't stand back all innocent eyed.
I'm intolerant of even the "mistake" excuse. Setting: You are the U.S. military in a Muslim country that has been lawless for quite some time, and you are fighting the Taliban. You are very cognizant of the low education level of the inhabitants, and their tendency to emotionally react to everything termed religious.
You have these Qurans that you want to dispose of. What do you do? Put them in a container, ship them out, and dispose of them elsewhere? OR, BURN THEM? Really, is the U.S. military THAT stupid?
Edit: A historical note. The reason we are fighting the Taliban in Afghanistan is because, as the world's oil whore, the U.S. allowed the Saudis to export their extreme Wahabbism to Afghanistan. Keep in mind, we are the ones that funded, armed, and trained Osama bin Laden in Afghanistan because we didn't give a damn what he did as long as it was against the Russians. I attend law school with two Afghani lawyers. My school has the U.S. State Department contract to try to rebuild their judicial system. One of the reasons we received the contract was because Washington state has such a good working relationship with the Indian tribes. So, the Afghani lawyers have been traveling to the tribal meetings with hopes that they can implement a similar program in Afghanistan to try to blend the uneducated tribal factions with the few remaining educated in the country. They want their country to be like it was back in the 50s. http://www.foreignpolicy.com/articles/2010/05/27/once_upon_a_time_in_afghanistan?page=full