What ISIS secretly wants - and most other religious organizations want the same - is to kill their permissive "mother" (modern civilization) and have sex with their absent, abusive "father" (god), which is an interesting twist on Oedipus complex described by Freud. Sexual repression is one of the main causes of fanatism and one of its main tools.
"The fact that a believer is happier than a skeptic is no more to the point than the fact that a drunken man is happier than a sober one." - George Bernard Shaw