They are functioning in the same manner for the same goals and they DO work together as we have seen in Iraq. There is danger in pretending there is a difference.
Fanaticism is a description of the level of zealotry found in followers/members of any group, not just Fascism and its clones.
Actually, Hannah Arendt documented one of the truths of Fascism ~ it was not only evil, it was banal in its evil. She's the person who came up with the term "the banality of evil".
The term "fanaticism" implies something far different.
I am not sure what the point is in claiming that there is no difference between Shia and Sunni ~ that would be like claiming there is no difference between the Roman Catholic church and the Apostolic Charismatic Free Will Seventh Day Baptist church on the corner.