IS is about power and egotism, not religion
The glee with which they carry out barbaric murders tells us much about their callousness and lack of empathy. Their actions have nothing to do with religion, but, rather, are about power, control and egotism (see how they like to pose for cameras).
Their misuse of Islam to enact their wicked deeds is a shame on them, as is their penchant for coaxing the naive and the disenfranchised to join them in murder, mostly of their fellow Muslims.