A huge part of the problem is that they're not hijacking anything. The jihadists are reading the plain text of the Koran and the Hadiths and following them literally. Moderate Muslims typically have very little scriptural text to stand upon when decrying ISIS and its treatment of infidels. ISIS can be more easily argued to be following the "most pure" form of Islam.
The fact that the crazy has metastasized and the crazy's adherents can't tell the difference, doesn't mean that we can't.
And the blend of eastern orthodoxy from my country has its own flavor, compared to the the general eastern orthodoxy branch, as we've also picked up a set of local customs and traditions along the way. Consequently I think this is why, even though atheism is on the rise and even though I'm what you could call an agnostic, I happen to believe that religion is ultimately good, as it's a part of the local culture, the local culture being a huge part of our identity.
But speaking of Christianity, our local christians tend to be a little xenophobe. And this I never understood why it happens, because you know, Christianity being about the teachings of Christ above all else, with those teaching inviting us first and foremost to love our peers and to be more tolerant. Skipping over the obvious that sometimes Christianity has nothing to do with the teaching of Christ, I personally think it's more about the true human nature. I believe that in essence a large part of the population is xenophobe, fearing and hating what is different and the material is always there to be exploited by a capable leader that can canalize all that potential hatred towards a common goal that can blur our ethics. After all, we should always remember the nazis, as that's the history that shows us how an otherwise civilized society can turn overnight if you press the right buttons, the anti-pattern we should steer away from.
Which brings me to the point that I wanted to make. I see a lack of tolerance and hatred even in many atheists, having the same potential for evil as everybody else, atheists who otherwise claim to be more enlightened. Not all of them of course, just like how not all Muslims are jihadists. And so I don't think changing the naming would make that much of a difference.
How do you argue which definition is more correct than the other? By Historical precedence? By how we interpret the teachings? By popularity? It just seems like the definition of the religion itself is so amorphous that it is very susceptible to terminology hijacking.
Would it do the Muslim population more practical good if they started distancing themselves away from the term "Muslim" and called themselves something different to make the distinction more impactful in the eyes of the public?