All of this is being done in accordance with Islamic law. Islamic law (Sharia) is based on the Qur'an and on Muhammad's example. All of the things that ISIS and Boko Haram are doing have also been done by Muhammad. In fact, I believe that Muhammad has done even worse things. However, in the Western world we are considered to be hateful and islamophobic if we tell the truth about Islam. Yesterday I was banned from a forum for saying that the difference between moderate Islam and radical Islam is not an ideological difference, but a difference in the degree of commitment to the cause of Islam. Radical Muslims are simply devout Muslims who follow Muhammad's example as much as possible. They are the true Muslims.
Sometimes I feel bad for saying these things, but what can I do if they are the truth? If we keep ignoring these truths, it will be our grandchildren that will kidnapped and enslaved by groups like Boko Haram or ISIS.