Of course, its seems a total evidence that ISIS (or Daesh, in arab) absolutly have nothing to do in common with anarchism or any kind of anarchists.
The only link that could be made is by the anti-terrorist policies that tend to mix things that have nothing in common as long as certain acts should be considered "terrorist".
That being said, I think it's very important to reconsider the question of this "proto-State" or movement (call it whatever you want) out of the emotionnal plague and wave of paranoïa instilled by the States, the medias, of western countries that have been targeted by violent attacks claimed by ISIS or other violent religious reactionnary of fascist-alike organisations.
As we know, the fear that is produced by blind mass murder or any kind of violent attack against random people, even being in itself scarry and horrible, would inherently be subject to recovery by politics and the state (especially its repressive forces).
In addition, it must be recognized that -as terrible as it should seem- the violence of the attacks of ISIS against people in the western world have nothing in common with the brutality and horror of what ISIS is actually doing in Iraq and elsewhere in the middle east. The actual iraqi governement, that is not even controlling a half of the country, is now declaring that what ISIS is doing could be simply called by its name : a genocide.
The ideology of ISIS is called "Takfirism", and its rejected by the vast majority of muslims, and even by organisations like Al Qaida (or at least the original "headquarter" that didn't pledge allegiance to Al Baghdadi, because some others did), not only because it's "too extreme", but also because it goes against a lot of the basic principles of Islam as a religion.
What I mean is that for muslims, and regarding to the islamic tradition on a historical point of view, it's not only a question of "who is the most extremist" or "orthodox", because there is a concensus about the fact that takfiris are less orthodox than other groups as long as they are pretending that "the necessity of the holy war" justifies to bypass the very principles of islam concerning what is haraam (forbidden) and halal (authorized or "licit") for muslims in the Quran and the sunnah.
Also because ISIS claim to be the "state of the ummah" (aka the whole muslim community), but that the vast majority of the ummah does not recognize itself in it. To make a simple comparision, it's exactly the same problem than far right and religious nationalists groups claiming to act in the name of "all christians" or "all american people" (for exemple) when the vast majority of these people don't support them.
To give an illustration of this problem, we could talk about the fact that most of the countries where islam is the dominant religion, even in islamic states (more or less authoritarian), the concept of "dhimmitude" is still applied to non-muslims. The idea is based on Quranic verses and the islamic tradition that recognize that non-muslims (especially believers) must be protected as long as they respect the law of the country and pay their bill (to sum it up).
I'm not a specialist of Islam, but basically I think I'm not mistaken about the concept. More or less, its the islamic version of the law on foreigners. It's often caricatured by islamophobic pranks (most of them being religious or non-atheists), but replaced in the context, comparing the way other religions are generally treating people considered "infidels" it should be considered as something less worth than many others. Of course, it always depend in the various situations of very different places in the world, and the way it's applied. But whatever...
The fact is that in principe, ISIS mainly considered dhimmis as ennemies, and those who don't pledge allegiance to the tyranic law of the Califate (the territories claimed by ISIS) and to Al Baghdadi aka "the Calif" (the big boss of ISIS) are condemned to death or slavery, which is of course considered a crazy thing by most of muslims.
I think it's also important to recognize, especially as people living in the western world (with its specific cultures, and paradigms) and even as atheists, that sadly (because it's often a forgotten fact) the first victims of ISIS in term of number are themselves muslims (considered infidels because of their specific practice of Islam) on the one hand, and non-muslim arabs and minorities on the other hands. Media often talking about these last ones as "christians from the east" or maronites, and yezidis.
And of course, ISIS says that killing or enslave all these people is in accordance with the Quran and "the necessity of the holy war", but the fact is that they have a very personnal way to interpret the Quran. And also they say that there is no possible "interpretation" of it, and that what is written must be followed to the letter. But of course they only choose the passages that fit to their practice and ideology.
To be more specific, many muslims accord themselves on the fact that the Takfiris (aka ISIS) are totally rejecting the principle of hermeneutics, which is the philosophical and religious theory that promotes the interpretation and exegesis of the texts, that -according to this principle- are always to be considered relatively to their historical period, and specific conditions, and not applied "by the word" (still always subject to interpretation).
Otherwise, it should be said as an evidence that most muslims consider slavery, murder of dhimmis (or non-muslims believers) or in general, etc... to be considered deadly sins in the Quran or even the Sunnah (the islamic tradition in accordance to the live of muhammed, aka the prophet), especially when its used as a form of propaganda or a way to force people to convert. And this because of a simple idea : you would never know if the conversion is sincere when its forced... Exactly like you can never know if something is "true" when confessed under torture, for exemple.
All this being said, I know that the temptation to criticize islam as a specific religion is very tempting for western atheists, but to me, it tends to easely degenerate in commonplaces, almagams or even racist prejudices. I know that islam is a religion and not a "ethnic" category, but in a similar way as with antisemitism, the racist clichés tends to amalgam religious beliefs, physical appereance and cultural specificities. And even not being racist, reducing the question of ISIS, or what media call "islamism" to Islam as a religion generally tend to reductionnism that make us miss a lot of important elements, if not the essential ones.
Before being a religious organisation, ISIS is mostly an army, and a rich warmongers international company at the age of global capitalism, like many others before them. We also must keep in mind the Al Qaida (their "ancestors") was founded by billioners, and not "simple poor peasants" and "romantic warriors".
This last image is the one that ISIS, and many organisations of the same kind are trying to give of themselves. Most of the time, the managers of the organisation are never in the first line when it gets to armed conflicts.
From this point of view, it has been said that Al Qaeda was mostly a "startup" of international "terrorism", or simply warfare (which is also a business before anything else), and that it simply degenerate into a network of mercenaries. The "schism" between Al Qaeda and other little organisation on the one hand, and ISIS on the other hands should be reconsidered on this simple level. Ideology and religion quarels being always or most of the time questions of power in general, and money in particular.