The problem there, ,LustfulBride, is that there isn't really anyone in Islam who can do that. I'm not sure if you're religious or not, but imagine you are and further that I'm a member of the same religion. If you do something to piss me off I can regally declare that you're excommunicated, sure. But who the fuck am I? Even if I am the head or an influential person in my own sect and can get all my mates to agree that you're a stupid stupidhead and totes shouldn't be allowed in our gang I still have no sensible authority to declare you not part of the religion in any way that exceeds futile rhetoric.
Yeah - Islam is structured more like, say, Protestantism than Catholicism; there is no Islamic Pope with supposed authority over the entire religion (only God/Allah gets that privilege). Hence the rampant sectarianism.
And the cause for Daesh to become what they are , is because of the gap between Islamic countries as a whole. During the rise of the Islamic nation during the Abbasid , Omayyad and the Rashidun , there used to be a ruler for that nation. A single ruler , named Khalifa ( In English pronounced as Caliphat. )
Daesh claims they are the Caliphat now. And setout to correct everything. Well that's what they think , but they're just set out to fulfill that sick twisted desire to cause war.
If there was a ruling Muslim figure , the chances of Daesh and the like coming to existence were slim. ( Not impossible , but much lesser than now ).
But that will not happen , due to how international politics works now. To be under a singular Islamic rule , means to give up authority over state to someone else. You wouldn't see Saudi Arabia , Egypt , Iran or anyone else giving up their authority over their land and become a mere representative to someone else.
And this is just how politics works. Religion itself doesn't really function the way most westerners think it does. If a Saudi Mufti produces a fatwa about X. A Mufti from a different country might disagree with him , producing a fatwa that contradicts it. So Islam's practice in general isn't a 100% parallel in all countries.
To unite Muslims under a single rule is practically impossible. Besides its been foretold in many Hadiths that Islam itself will fade.