As far as just in America, I am totally for free speech. Now if you want to hire someone for something illegal, nobody is going to duct tape your mouth shut, but they WILL use it as evidence to prove you were attemping to do something illegal.
For at a theatre just saying "Fire" in itself isn't necessarily a bad thing. Yelling it and causing trouble though will. It is seen more as a violation of a law than just saying something bad or offensive. Why not set off a siren or alarm in the middle of the theatre when there is no danger, you would probably get the same result without even having to use words.
Now there are small things of censorship like laws against public nudity and excessive swearing, but who wants to see a naked 300 pound wrinkly grandma with saggy boobs smoking weed or drinking and saying obscene things to Salvation army volunteers in front of a 7-11 (or other store)?
There are definately some things that are censored, but from my viewpoint it is hard to argue with them. I've lived with these rules most my life and they seem to make sense. If they weren't there though, the only one I see problems with is using speech to do illegal things. In most countries it is a standard to wear at least some form of clothing. As far as swearing, I have no idea how other countries handle that. You can get sued here though, whether or not there are actual laws against it.
Now I never saw this cartoon, and I don't even know what publication it is in, but I don't care how offensive it is it does not justify violence. If someone yells insults at you, and you beat them to a pulp, you're the one who got carried away. You could just add people to your "ignore list"

Nobody is forcing you to read the damn cartoon. It's like looking at porn. If you see some porn by accident while surfing a warez website, are you going to burn down the website owner's house? Arson is a crime, so if you would, have fun in prison.
If I see that ugly naked grandma cussing me out, I'm not going to beat her to a pulp, I'm just going to leave the area very quickly.
These people are just getting carried away. As people have said before, some Muslims are going to cause problems and resort to violence, just as some Christians do. It's just part of the group, not the whole group.
Now if they want to protest, I'd freaking let them. That's also freedom of speech. But if they want to protest with directed gunfire and explosions then they need to be dealt with. Nobody should die over a damn cartoon.