ISIS are Sunni and follow an ultra-radical Salafi-jihadist ideology, which is a strict, literalist interpretation of Sunni Islam. They consider Shia Muslims, Sufis, and other Islamic sects “apostates” and justify attacks against them as religiously sanctioned. ISIS label Christians and Jews as “People of the Book” and according to their extremist interpretation, anyone who refuses to submit to their version of Islam must convert, pay a tax, flee, or be executed. Other religions such as Yazidis, Zoroastrians, Hindus, and the likes are considered idolatrous and heretical thus justifying enslavement, execution, or forced conversion of those groups. Muslims make up the majority of victims simply because they make up the vast majority of the population in ISIS-controlled areas and are caught in indiscriminate attacks. Minority religious groups (Christians, Yazidis) suffer far higher rates of targeted killing and atrocities relative to their population.
I am Atheist and I think organized religion as a whole has no compatibility with our world today and particular the more violent and extremist sects of all the major religions