Charlie Hebdo practices the same kind of free speech that people on the right around the world tend to fixate upon. They make a statement visually which will offend a huge number of people in order to make a point which is directed at a small group, then when people express outrage they double-down as a way of saying "fuck you, I can say what I want". That was the main reason they went so hard in on depictions of Muhammed, they were telling extremist shitsticks that they weren't allowed to tell them what to do, but in doing so they also offended a lot of perfectly reasonable people.
It's perfectly valid, but I don't think anyone should be surprised that people find it offensive. You can't just shut people down with "it's satire", that doesn't change the fact that it's offensive. Charlie Hebdo can keep doing what they're doing, some people will appreciate it and some people will think it's vulgar. That's what real freedom of expression is about, promoting a truly diverse marketplace of ideas and opinions.