Their name should be ESIS not ISIS. I cringe that they use “I” for Islam. The correct letter should be “E” for evil. Killing of innocents is non-Islamic. “There’s no compulsion in religion…” (Quran2:256). “…to you be your religion, to me be mine” (Quran109:6). Muslims are to live in peace with people of other faiths.
In pre-Islamic Arabia, female infanticide was widespread. This was made illegal with Islam. There’s nothing Islamic about groups who don’t respect women. Extremism is non-Islamic.
Islam’s Prophet warned his followers against all religious extremism. There’s only evil in this group. They’ve no right to use the word Islam. There’s nothing Islamic about them. They’re truly ESIS not ISIS.