ISIS is a core element of a vile "double-game" engineered by the West. On the one hand, ISIS is presented as the "enemy" --- which takes very little convincing --- while on the other hand, the West uses ISIS as "strategic assets"/proxies to destroy "non-compliant" sovereign countries abroad.
All of this serves to create an enemy based on racism and disinformation -- necessary components of all imperial war crimes.
The engineered "enemy", in this case, our ISIS "assets", also serves to vilify all Muslims. Islamophobia is a useful instrument that enables the process of illegal invasions abroad.
Meanwhile, the Koran's teachings are diametrically opposed to anything that the West's ISIS mercenaries might profess to be part of their belief system. Chopping off the heads of innocent civilians, many of whom are Muslims, certainly does not align itself with teachings from the Koran.
Former NATO Commander, General Wesley Clark was very transparent, during a Democracy Now episode, that the US had planned in advance, to "take down" (illegal regime change) seven countries in five years: Iraq, Syria, Lebanon, Libya, Somalia, Sudan, and Iran. War plans always precede propaganda campaigns.
So, the diabolical purpose is to create widespread Islamophobia, and to continue to create false (and ever-changing) pretexts for permanent war, looting, and the mass slaughter of innocents. Targeting civilians, creating murderous chaos, using terrorist mercenary proxies, and installing puppet regimes are all part of Western military doctrine.
Criminal Western propagandists have confused the Syrian crisis to such a degree -- by design -- that the self-evident truth of their military strategies have now been obscured.
Professor Tim Anderson's recently published e-book, The Dirty War On Syria, however, provides clear, well-substantiated evidence of the truth. In Chapter Eleven, "Washington, Terrorism, And The Islamic State," some of the supporting evidence includes these references:
As early as 2006, the West was trying to "destabilize" (ie destroy) Syria.
A 2012 Defense Intelligence Agency (DIA) document clearly states that the Salafist, the Muslim Brotherhood, and AQI are the major forces driving the insurgency in Syria" and that, "the West, Gulf Countries, and Turkey support the opposition, while Russia, China, and Iran support the regime." (The term "Salafist" refers to ISIS and "AQI" means al-Qaeda in Iraq.)
General Martin Dempsey disclosed in 2014 that "I know major Arab allies that fund them" (referring to ISIS). The allies in this case includes Wahhabi Saudi Arabia and the Gulf countries).