Thats because islam teaches violence. For example:
Sahih al-Bukhari 6924—Muhammad said: “I have been ordered to fight the people till they say: La ilaha illallah (none has the right to be worshipped but Allah), and whoever said La ilaha illahllah, Allah will save his property and his life from me.”
Qur’an 9:29—Fight those who believe not in Allah nor the Last Day, nor hold that forbidden which hath been forbidden by Allah and His Messenger, nor acknowledge the Religion of Truth, from among the People of the Book, until they pay the Jizyah with willing submission, and feel themselves subdued.
Qur’an 48:29—Muhammad is the Messenger of Allah, and those who are with him are severe against disbelievers, and merciful among themselves
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