But, if I were to take the liberty to express my own opinion, I would say honestly, I think both parties were at wrong here. First that their have been many instances in the life of our prophet, when he faced not just harsh but inhuman treatment, specially in his hometown of Mecca. Yet he never lifted a finger or even wished for those people to get hurt (there is specific mention of this in Islam). It is against the moral of our religion to engage in such "eye for an eye" notions. Yet people (like the 4 suspects) who are not aware of their own religion and the finer lines tend to do these things when agitated or pushed in a corner.
On the other hand, Religion is a personal affair. People are serious about it, be it any religion. People live and die by the religion, it is the very guide of majority of the people in this world. And if someone portrays something so closely associated to people, it is a kin to playing with their feelings. And that is where things start to get ugly, and such mishaps happen.
Satire is accepted in Islam, as evident from the semi-fictional writings about Mullah Nasruddin.
http://en.wikipedia.org/wiki/Nasreddin
But the level of Satire in question here, was perhaps too much. Besides the additional fact, that impersonation/impersonification of Prophet Muhammad is highly condemned in Islam. Even if we are to write a play on factual things about him, it is prohibited to have someone portray him (even for a good/just reason). To say that in other words, to Muslims, a graphical satire is acceptable on anyone except the prophets, which includes Moses, Jesus, Abraham, etc. Yet, if someone does want to amuse himself or exercise his liberty knowing that it is something that hurts us, we simply have to ignore him. Things should not go further than that.
People in the west have indeed respected this, as seen in the movie:
http://www.imdb.com/title/tt0074896/
Let us understand each others liberties as well as sensitivities, so that by standing firm together, we will all make a better society, both in France and the World.