To understand the danger posed by Islam, one must first understand its Islam. And I don't mean its spiritual appeal, because Islam is not a particularly spiritual belief system. It is not really much of a belief system at all, so much as it is a tool of social organization. Because Islam is far less concerned with what people believe, than with what they do. It is not so much of a religion, as a means of ordering behavior within a society along particular lines.
The contents of the Koran and the Hadiths are for the most part wholly unoriginal, a clumsy melding of regional myths and customs, with bits of Judaism and Christianity mortared into the whole mess to give it some sense of history and order. Islam's obsessive focus on Mohammed above all else, betrays the bankruptcy of a religion that had no other prophets that they hadn't "borrowed" from pre-existing faiths, and after rolling them in, proclaimed that Mohammed was the absolutely last prophet, and no others need apply on pain of being beheaded. But none of that is the point, because Islam's purpose was not religious, it was social. Islam may have had nothing new to offer religiously, but it had something very important to offer socially, unity. And that one compelling idea dominates Muslim thinking to this day, and exemplifies Islam's appeal to the Muslim world.
The Mecca and Medina both of Mohammed's day and of the present day, was a world dominated by tribal clans and families. There was no larger principle besides working for the benefit of your own family. No trust was possible even between neighbors except premised on the threat of retaliation from one's own kin. To advance required family backing. The clan was everything. The individual was nothing. Justice was meaningless. Law was a means of settling disputes between families in order to avoid vendettas and conflict.
Mohammed's Islam by contrast promised a supreme unity above tribe and clan. The unity of the true believers. This of course is a universally common promise made by cult leaders, and has a timeless appeal to the disenchanted looking for a higher principle and a new identity. So Mohammed was certainly not the first or last "prophet" promising a new order for the believers in which the old social order would become meaningless, and they would be the ones to end up on top regardless of rank or birth. That has always been actually a major recruiting tool, particularly for apocalyptic cults. But Mohammed's version had the largest wingspread, as a billion Muslims today still wait for the entire world to be transformed into a "perfectly just: Islamic society under Islamic law.
What Mohammed offered with Islam was a new identity for Arabs, as Muslims. As tribes and clans they would always be divided and quarrelsome, but as Muslims they were supposed to form into a perfect unity through their submission to Allah, by way of old Mo himself. And while the power of that appeal may often be lost on Westerners, one only need look at the average present day Arab nation, whose governments are familial, where the bureaucracy and military hierarchies are composed of the sons of families who have relationships with the families who run the entire system.
Beneath modern sounding titles such as President or Prime Minister, the old tribe and clan relations still dominate the region. To rule one must have their support. To get their support, one must trade favors. And so under the aping of Western manners, titles, military uniforms and office buildings-- the Middle East of today is not so different from that of Mohammed's time. Except the Christians and Jews are mostly gone. In their place is country after country full of Muslims, which are ruled by governments that are as nepotistic, corrupt and dysfunctional as you would expect from people who have no higher loyalty than to the clan.
The Islamists of course can never deliver on their perfect "Islamic society", because their own leadership is just as corrupted as the rest of the Middle East. But by constantly holding out that promise of a perfect society and the brotherhood of all Muslims-- they capitalize on the existing discontent much as Mohammed himself did. And if they ever succeed in taking over, the same sort of thugs that Mohammed himself employed and reward with the loot of his murdered victims, will suppress dissent far more ruthlessly than the previous authorities their "revolution" over threw-- as the Ayatollah's Iran and the Taliban's Afghanistan has aptly shown.
This then represents the problem with trying to apply democracy to the Muslim world. Democracy on top of the clan system results only in representation for the clan leaders, which is perhaps a step forward, but not that much of one. Since the clan leader is already the system and the clan is the process, democracy cannot displace him, just as democracy could not displace the DMV or the post office. But it can and will elevate the Islamists, because it is a useful tool for those propounding Muslim unity, who are naturally the only point of unity in countries where there is no other unifying idea except xenophobia and intolerance for the smallest divergences from the norm.
While a few Arab and Muslim countries have experimented with nationalism, theirs is a recent and thin innovation with no real history behind it. The borders of much of the Muslim world are the product of either European colonial mapmakers or, as in the case of Pakistan, enforced separations. They may have flags and anthems, and their leaders may dress in suits or military uniforms borrowed from Westerners, but these are poor facades, and their own people know it. Nasser's Arab Socialism and Baathism were poor copies of European ideas implemented by professional elites and virtually meaningless to the ordinary Arab. They did not bring unity, only more war. (Islamism will of course do the same, something that the prolonged bout of Al Queda atrocities in Iraq and Jordan have communicated to a small percentage of the region's inhabitants.)
But among all this violence and injustice, Islam continues to hold out the golden promise of a unified Ummah, on terms espoused by a cult leader on the primitive terms of a millennium and a half ago. Because it represents magical thinking, it will always remain more appealing than real progress and reform. While progress and reform take work, the magical solution of Sharia promises to make everything just and right as soon as it is imposed. It is also why Muslims in the region will continue to see democracy as a means for imposing Islam, rather than as an end in and of itself. Because simply injecting democracy into a region that lacks an understanding of a theory of government based on popular representation, turns into a tool for imposing the magical solution of Islam.
Turning to Western Muslims though, one might ask why they embrace Islamism even more aggressively than they do in their own home countries. But the answer is rather obvious. The multicultural societies they are asked to be part of are even more fractured and divided than at home, but without the relative structure of tribe and clan. Studies have shown that in multicultural societies there is less trust between neighbors, which is an inevitable outcome of weakening the natural human bases for connections within a neighborhood or community. Islamism is even more in demand in such a fractured system because it promises absolute unity, where now there is only a multitude of divisions.
The idea of Islam co-existing with a diversity of religions and beliefs is a bit of paradoxical stupidity. Islam was created precisely to supplant a diversity of religions and beliefs by people who wanted to find unity through one supreme system. The rise of Islamism in the West cannot be negated by multiculturalism-- ITS POPULARITY IS A REACTION TO MULTICULTURALISM. The Muslim who finds himself having to deal with Christians, Jews, Sikhs and Hindus on a daily basis, who has to navigate a complex and often contradictory system of social rules and codes naturally longs for stability and simplicity, and he finds it in the most radical interpretations of Islam.
The final benefit of Islam of course is that it makes the Muslim in the West immediately superior to the Westerners. The Muslim Doctor is not only immediately better than his Western colleagues for being a Muslim, but even the lowest doletaker is better than all the infidels. And better than his Muslim brothers who have compromised their religion by becoming too British. He finds a new solidarity and self-esteem by plotting to overthrow and conquer this nation of infidels. And meanwhile back in Saudi Arabia or Iran, the same chaotic cluster of families and clans finances the Islamists, in order to keep their dangerous ideas away from their own throats while using them as a weapon against the West, watch and laugh.