Have you noticed that whenever there is a terrorist attack that certain people rush to the defense of Islam saying "Well there are extremists in Christianity too" No doubt there are professing Christians who have committed despicable and inexcusable acts but it really misses the point entirely. There is something intrinsic to teaching in the Quran and early Islamic history that is somehow being missed in these online discussions.
Muhammad directly taught, in many circumstances, that we ought to kill or subjugate our enemies (e.g.. Surah 9). Christ by example taught we ought to die for our enemies and liberate them ... It is recorded in history that Mohammed had murdered dozens of his enemies by the time of his death. Jesus, having killed no one, died to reconcile his enemies to himself, calling us to love our enemies and turn the other cheek when we are persecuted by them. Following these teachings, the first 500 years of Islam was a story of bloody conquest. The first few hundred years of the church was one of weakness and severe persecution for the followers of Christ, not conquest. So we can see that the teaching of the two heads of these faiths could not be more sharply contrasted. One leader in many circumstances gives justification to sacrifice others, the other only justification to sacrifice self for others.
This is certainly not to deny that there have been professing Christians in history who have murdered others. There have been. But, if they read their bibles, they knew they were acting in disobedience to their Lord. (Christians are capable of sin like anyone else). But those Muslims who kill can appeal to a wide variety of Muhammad's teaching to justify murder. So the media portraying groups like ISIS as not true Muslims is a clear distortion of the truth. Certainly they do not represent all Muslims but they're not teaching anything much different from the founder of their faith.