It seems justified to try and understand the situation as an offended Muslim would see it. The following points are just some that come to mind, in the broader context -not just about this particular incident, but generally how a Muslim would feel when his/her Prophet is insulted whether it be through cartoons (as in Denmark a few years ago) or a film or in any other manner:
1. Islam is NOT against scholarly free speech. In fact, quite the opposite. It is common practice for Muslim scholars and Mullahs in Islamic institutions (such as the holy city of Qom in Iran) to have a civilized and scholarly discourse regarding questions, objections, and condemnations that might have arisen about their Prophet anywhere in the world. So long as the conversation is free of deliberate provocation and insults, Muslims are very open to arguments. The concept of gaining knowledge through discourse and scholarly disagreement is not only welcomed in Islam, but even actively promoted in Islamic tradition. This is easily verifiable -all you need to do is search the internet for countless academic discourses that are underway between Muslim scholars and those who refute them, without any ensuing violence or outrage.
2. The love of Prophet Muhammad in Islam is insurmountable. Everyday, as part of the prayers that each Muslim individual must preform, the sentence "Peace (and Blessings of Allah) be upon you Oh Prophet" is repeated at least five times. The prophet is so respected that it is very rare for anyone in Islamic countries to refer to him as plain "Muhammad" without following his name with the phrase "peace be upon him and his (beloved) family". Depicting the prophet -even if it is with the holiest of figures- is not permitted. Let alone insulting him.
3. 'Deliberately insulting' the prophet is very different than questioning him through free speech. Even if the insult is done unknowingly, ignorantly, or inadvertently, there would be no such outrage. Those who have insulted the Prophet could easily issue a statement saying that they are sorry and have repented -the outrage would simply die down. However instead of apologizing for their actions, those who have provocatively insulted the Prophet are full-heartedly reaffirming their stance. [interestingly Muslims are even more open to the apologies of foreigners than the apology of a Muslim or someone who is born into Islam (as in the case of Salman Rushdie). This might be because they think a Muslim should know better than to insult the prophet in the first place; and that someone from a different background and another belief system can be dealt with much more leniently].
4. To a devout Muslim, 'deliberately insulting' Muhammad is much worse than killing him. This is not an exercise of free speech, it is an act of war. When US officials state that "there should be no debate about the simple proposition that violence in response to speech is not acceptable" they simply don't understand the severity of the situation. In her religion, culture, and society the US official which makes such a statement has simply never felt (or seen anyone feel) the level of compassion and devotion that Muslims feel towards their prophet; therefore the reaction is incomprehensible for her.