I kinda like how you phrased that question.
First "ISIS" is two things: The "islamic state" is a place. or maybe an evolving territory on a map. More importantly, it represents the caliphate, or cancerous spread of islam worldwide. Since it's rather silly to ridicule a "place", let's agree the ridicule is regarding the latter.
Their "prophet" teaches that the Koran is the pure word of allah, and can't be diluted, parsed, or disobeyed. AND, it teaches that apostasy is punishable by death. If I recall correctly, apostasy is considered worse by muslims than disbelief. That is, once you're a muslim, if you backslide or change your tune (or even question their playbook), you're worse than a Christian or Jew. And they are commanded to expand their "religious" dominion. Even if you're not a head-chopping jihadist, you're commanded to be on the lesser-jihad bandwagon.
Martin Luther posted the 95 Theses (on his blog) and proclaimed that the common man could read and interpret the Bible just as well as could those in the priesthood, which set about the Reformation and sucked all the power (though it took a while) from said priesthood. Conversely, you'll never see islam toned down or reformed. They be all about tha power.
Some evidence in support of skepticism? Consider exhibit A:
Charlie Hebdo...Exhibit B:
Salmon Rushdie...Or exhibit C, this little girl, who just wanted to flee an arranged marriage: