Muhammed 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 killed 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. 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 sacrifce 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 killed others. There have been. But they were knowingly 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 Muhammed'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 are not teaching anything much different from the founder of their faith.