In my opinion, any ISIS member can be compared to the garbage of this world. I very much doubt whether they are human beings at all. Even calling them an animal would be an offense to the animal.
Many ISIS members are converts to Islam. In his book Sefer Kuzari-The KUZARI, 1:115, Rabbi Yehudah HaLevi defines the Jewish concept of someone converting to Judaism:
In Judaism, the way we make converts to our Torah into Jews is not through utterance a word (like in Islam). It is rather through their acceptance of acts which are burdensome to the soul, which include purification, study, circumcision and the observance of our many laws and customs.