Everyone seems shocked when Muslims riot over a poorly made Youtube video or some silly cartoons. But violent responses to criticism are a tradition in Islam, and Muhammad himself started the tradition. Let's look at an example.
A man named Abu Afak was more than a hundred years old when he decided to write a poem about Muhammad, who was dividing people and causing them to kill one another. Here's the story of Abu Afak's death:
Abu Afak was one of the B. Amr b. Auf of the B. Ubayda clan. He showed his disaffection when the apostle killed al-Harith b. Suwayd b. Samit and said:
Long have I lived but never have I seen An assembly or collection of people More faithful to their undertaking And their allies when called upon Than the sons of Qayla when they assembled, Men who overthrew mountains and never submitted, A rider who came to them split them in two (saying) "Permitted", "Forbidden", of all sorts of things. Had you believed in glory or kingship You would have followed Tubba.
The apostle said, "Who will deal with this rascal for me?" Whereupon Salim b. Umayr, brother of B. Amr b. Auf, one of the "weepers", went forth and killed him. (Ibn Ishaq, Sirat Rasul Allah, p. 675)
Hence, Muhammad's followers understood that people who criticize Islam or Muhammad must be killed. Soon, Muslims were free to kill anyone who made fun of Muhammad:
Sunan Abu Dawud 4348—Narrated Abdullah Ibn Abbas: A blind man had a slave-mother who used to abuse the Prophet and disparage him. He forbade her but she did not stop. He rebuked her but she did not give up her habit. One night she began to slander the Prophet and abuse him. So he took a dagger, placed it on her belly, pressed it, and killed her. A child who came between her legs was smeared with the blood that was there. When the morning came, the Prophet was informed about it. He assembled the people and said: I adjure by Allah the man who has done this action and I adjure him by my right to him that he should stand up. Jumping over the necks of the people and trembling the man stood up. He sat before the Prophet and said: Apostle of Allah! I am her master; she used to abuse you and disparage you. I forbade her, but she did not stop, and I rebuked her, but she did not abandon her habit. I have two sons like pearls from her, and she was my companion. Last night she began to abuse and disparage you. So I took a dagger, put it on her belly and pressed it till I killed her. Thereupon the Prophet said: Oh be witness, no retaliation is payable for her blood.
Sunan Abu Dawud 4349—Narrated Ali ibn Abu Talib: A Jewess used to abuse the Prophet and disparage him. A man strangled her till she died. The Apostle of Allah declared that no recompense was payable for her blood.
When Muslims become violent over criticism of their religion, they are doing exactly what their prophet taught them to do. Yet politicians and the media continue to assure us that Islam is a religion of peace, and that violence only occurs when terrorists "hijack" the religion.