As a left communist just wanted to say a few things...
There's a lot of debate around these shootings regarding the "freedom of speech" of the cartoonists. Everyone is in agreement that - sure - these guys have the "right" to draw whatever they want. At a certain level this makes sense.
But like everything else in capitalist society there are class implications of all these things, and surprise, surprise, they are the only things being left out of the popular discourse on the Charlie Hebdo murders right now.
All the terms I've just written that one normally glosses over - freedom, rights, etc. - these are all privileges handed down by the bourgeoisie to everyone else. So when we talk about "freedom of speech" in capitalist society, we're just talking about the privilege to talk about things the ruling class is cool with us talking about. This "right" disappears very quickly in many situations, which is why I call it a privilege.
So how to deal with this? I think as communists we have to reject the notion of "free speech" entirely. Not all speech is free. Some speech is meant to be oppressive and we should oppose it. This is the framework for saying, "fuck no nazis dont deserve the right to march freely in the streets", and also "yes people can draw whatever they want" as long as it isn't repressive to others.
Yes, what is repressive and isn't will always be a matter of controversey, but I would hope that in an internationalist society without cut throat imperialist and class tensions that these issues could be solved with intelligent discussion and words instead of bullets.