Narrative and contexts are extremely important, in this case, Islam has been historically (and still is) of the strictest religions (if not The). With precisely described and followed rules for entering (conversion), and exiting (death is the only exit on papers, but majority are quite moderate and the worst you'll get is a disappointed kick in the butt by your family), and about "universal" way everyone should live their live.

And specifically due to this "strictness" (easy to convert and "impossible" to break out) we see the "popularity" of this religion on the World's Map, and also due to this "strictness" modern views and prejudices have been formed as it is very easy for a small group of extremists to take it over the top.