We have to realize that Islam and Christianity are significantly different only in their practices, rather than beliefs. It is largely because of the practitioners that conflicts exist between the two ideologies, both in the past and at present. As usual, it is the disordered nature of man that allows these differing perceptions how the ideology should be practiced. And it is man's predisposition toward violence that accounts for all the deaths and destruction wrought over the ages. This should aptly explain the Crusades, the Moors overrunning Europe prior to it, the Inquisition, present-day ethnic cleansing, and of course, the present stand-off. We should remember that man left on his own is predisposed toward violence and evil, even Catholic theology would confirm this.
A growing body of nascent scientific studies about consciousness, point to how man has over the ages evolved and developed his own individual consciousness from a prior well-ordered group consciousness, necessitating the formulation and implementation of codes of rules and punishment to keep him in check. It is society's role to mete out punishment when man strays from the norm. While the US has initially pre-empted this role, it has now involved the entire civilized world with the coalition that it has formed and its open declaration of war against worldwide terrorsm.
We also have to be discreet and quite discriminate when we use the term Islamic fundamentalist for the practitioner’s understanding of fundamentalism is quite different from the connotation we have popularly assigned to this term. For them, fundamentalism is adherence to traditional beliefs and mores of their ideology - thus, the continued usage of traditional clothing, the use of facial hair as a symbol of piety and reverence, avoidance of alcohol, traditional rituals, temperance in most things we take for granted, etc.
Any practitioner who advocates hate and violence as a valid means for promoting causes, even righting past wrongs, cannot rightly be called fundamentalist. He has to be an extremist at least, and at worst, deranged.