Unfortunately, I don't suspect dethroning 'preachers' will happen any time soon for one reason. The overwhelming issue is that in Islam there is no central authority (akin to the Vatican for Catholics) that regulates the dissemination of Islamic scripture; there are a number of competing—all of which incessantly fight for influence—'schools' of Islamic jurisprudence, and they either slightly or starkly vary in their takes on the meaning of scripture. Some are Maliki, Jafari, Ibadi, Hanbali; Hanbali in particular includes—although some reject this—Wahhabism (the most extreme doctrine, resulting in distortions of jihadism, tied to Saudi Arabia; some conspiracy theories insist that Wahhabism was invented within the Hanbali in the early 20th century by architects of Zionism seeking to weaken support for Palestinians, but—although Wahhabism is a notable divergence from work of early Hanbalites—these theories are largely baseless).
The lack of a central authority presents a problem because, then, preachers who preach distorted and fundamentally-incompatible interpretations of 'jihad', and expressly call for violence and terror rather than peaceful coexistence, face no risk of being punished or excommunicated (unlike the Vatican, which can excommunicate Catholic priests that refuse to faithfully abide by accepted interpretations of the New Testament in their sermons). So, the net result is that there are a range of preachers across the Islamic world who give sermons of varying degrees—anything from generosity, tolerance and coexistence to violent and anti-West jihad; and there is no methodical and consistent means of challenging their 'authority' within the religion itself; only the state can do this, but doing so in the West is tricky and may cause alienation.
In light of recent attacks, I think a number of remedies are in order:
<1> Sensationalist media or tabloid papers, such as the Sun Media in Canada and the Daily Mail in the UK, need to quit catering to their readers' vulnerabilities, particularly evoking widespread fear and stoking hatred with their publications. That's a haphazard way to inform the public in their quest for solutions. I imagine, a lot of Daily Mail readers would solutions that include mass deportation, mass internment, or even, ethnic cleansing (which, I'm sure your call, has been attempted before, regrettably). Internment or deportation would obviously be effective in the short term; but they will actually only deepen the alienation and turn out to be more destructive. Ultimately, the scale of destruction in the aftermath could amount to ethnic cleansing. I would not call this out of the question because I have noticed that there is, at least online, a lot of nihilism and regression back to primitive, survivalist, responses to these perceived threats; the evolutionary adaption that allowed humans to be hypersocial and gave them the gift of reasoning—i.e. the neocortex or outer-most layer of the brain—is being bypassed with these responses. It's regrettable, but very human.
<2> I think tackling online radicalization, as the UK's embattled PM, Theresa May, briefly remarked, is a step in the right direction (despite the objections that may come from net neutrality advocates), but I don't think an online 'campaign' against radicalization goes far enough. The root cause of these heinous crimes is marginalization and alienation. It all begins with marginalization and alienation. There needs to be local, community-based, support programs and social initiatives to prevent marginalization; these need to come from both government and faith communities, and the government programs certainly need to include mental health.
<3> One particular remedy falls on the Muslim community. Muslims need to stop attending sermons and establishments run by preachers who preach these distorted versions or far-fetched interpretations. Why this is not happening sooner, I have yet to grasp. I imagine it has to do with laziness and culturally-ingrained lack of political enthusiasm from various African and Arab communities. Sooner or later, I figure, they will get moving.
<4> Finally, non-Muslims really need to try to resist the urge to generalize. They need to be reminded that terrorism is not limited to Islam and hasn't suddenly appeared in the 21st Century out of a void. It has been around for a very long time, as University of Chicago professor Robert Pape pointed out, and in various political and religious contexts. There are Buddhists groups who engaged in terrorism for religious causes. There is the present-day PKK in Turkey; France's right-wing La Cagoule at the outset and during WWII; and Canada's own, now-defunct, FLQ; who all used violence towards political ends—the definition of terrorism. It is inconceivable for 1.3 billion to be held accountable for the actions of a fraction of 'bad apples.' Much in the same way, Catholics are not violent and oppressive, or blameworthy, for the bombings by IRA militants and other religiously- and politically-motivated attacks against Protestant unionists; and, further, Protestants are not accountable for the religiously- and politically-motivated attacks against Catholics, perpetrated by the Ulster Defense Association militants who are Protestant; nor are Catholics accountable for the same attacks, and assassination of English royal and cousin to Queen Elizabeth II, namely, Lord Mountbatten, perpetrated by the IRA militants. Note that they are politically-motivated because unionists are a political group (they support the preservation of the union of Northern Ireland, Scotland, England and Wales) and religiously motivated because Protestants are a sect and oppose the other sect, Catholics, who account for Irish Republicanism (separation).
Interestingly, at one point in ancient history (around 5-600 AD), there was a school of Murjites (or 'the Postponers'), which was the most lenient school. As you may have imagined from their name, the Murjites believed in postponing any sort of judgment against a person until his/her end of life, when s/he comes before God in the afterlife (N.B.: I am just recalling what they believed; I don't necessarily share those beliefs). Their crux of their teachings is that there is only one judge of a person's deeds or misdeeds, and that judge is God; no human being can take God's role. Murjites, thus, would oppose labeling anyone a 'heretic' and oppose present-day Sharia courts that routinely pass judgment and dole out punishments against convicted 'heretics;' they would oppose violent Jihad because it is, by its nature, judgmental; in essence, they would oppose any act that harms a person in response to their beliefs because it would require judgment. Unfortunately, their influence quickly dwindled when, in later periods (by as early as 8-900 AD, I think), harsher and competing schools gained influence and deemed the Murjites, and their followers, 'heretics' and had the lot of them executed (ironically, in doing so, adherents of those opposing schools passed judgment against the Murjites and inflicted punishment). Apart from deferring judgment, Murjites also believed that any adherent to the faith who began taking steps to carry out a grave sin, such as murder, relinquished his/her status as an adherent.
A disclosure: I am of Muslim heritage and was raised by very lenient Muslim parents; but I identify as an agnostic and don't practice.
