Cartoons target twisted beliefs of extremists
If you pay attention to the content of the cartoons produced at Charlie Hebdo you will see that - just as in the case of the Danish cartoons at Jyllands-Posten - none of them are actually "about" the Prophet Mohammed.
Indeed, they could only be construed as being "about" him if they depicted something he is generally believed to have done or said.
Most of these cartoons satirise not the Prophet, but the beliefs about him implied by the actions of extremists.
The primary target of all such cartoons is the beliefs of extremists.
What they seek to depict is not the Prophet himself, but what the extremists' actions imply about him.
Lazily using the wrong language to describe them may well stoke hostility between people who actually agree with one another.