As I was reading this article about IS;
I really wonder who this IS is?
In Islam, it is forbiden to take innocent life:

“And do not kill the soul which Allah has forbidden, except by right.”
Quran 17:33

And, in Islam, religious differences do not warrant the taking of a life.

“There is no compulsion in religion”
َQuran 2:256

Hence, IS as an acronym cannot stand for Islam.
For a Muslim is not a Muslim if they go against the teachings of the Quran.