The Nazi party was a right-wing political cult, the communists were a left-wing cult. The Nazis in particular demonstrated the overwhelming power of organized propaganda to subvert the natural integrity of human beings. The Third Reich used radio, motion pictures, magazines, newspapers, front organizations, phony institutions, lectures, art exhibits, leaflets, posters, lectures, rallies, speeches, demonstrations, parades, and even early television broadcasts, to create an overwhelming illusion of credibility. A population that had not grown up with mass media, that had not yet learned how to filter it for meaning was easy prey.
And those lessons of propaganda and manipulation have not been lost on others. The techniques of mass-persuasion are reinvented every generation. Every new medium becomes another lever on the people. The purpose is always to attract those willing to adopt a specific mindset. Once a person accepts a mindset as the "true" filter of reality, he can be controlled by anyone who wields the machinery of the meme.
Here in the US, we've seen all flavors of political and religious cults. Our Constitution protects the right to believe any damn fool thing you choose, no matter how silly or embarrassing. Some of these cults have proven deadly to their followers; others have grown and claimed a pretense of credibility.
A cult requires a paradigm--or a meme--that disempowers all other memes in favor of itself. Many religious cults are based on a monotheistic meme: "I am the one true God, if you worship any other God, you will not go to heaven, you will be damned to Hell for all eternity." The intention and the result of this kind of meme is an evangelical mission on the part of the followers to obliterate (or at least make irrelevant) all competition. In its extreme form, this meme produces a holy war.
Because Islam, like Christianity, has a monotheistic meme at its core, Islamic extremists, just like Christian extremists, can claim this as a mandate for the obliteration of pagans, infidels, nonbelievers, heretics, blasphemers, and especially secularists. Secularism, by its very existence, places faith in a subsidiary position to such mundane matters as government, economy, culture, technology, and human rights.
Political cults -- like Nazism and Communism -- also need to disempower all other points of view as invalid. In those cases, political monotheism demands the assertion that capitalism or democracy are failed ideas. The Communists claimed repeatedly that capitalism was exploitative, the Nazis asserted that democracy doesn't work and their nation needed a "strong man" (a dictator). And this is why I have such a seriously jaundiced view of libertarianism, militia groups, fundamentalism, and occasional self-help movements -- so many of the adherents seem to function as if there are no alternatives to their way of thinking.
What we are up against -- what we are always up against -- is a way of thinking that does not acknowledge the validity of any other way of thinking.
Those trapped inside such a paradigm see those outside the boundaries as insane, damaged, failed, and in particular -- enemies. If a person cannot see any point of view except his own, he cannot respect the right of others to hold any other view, let alone any other rights -- such as free speech, freedom to assemble, freedom of the press, freedom of worship...freedom from fear.
Here in the United States, we operate in a paradigm that says all beliefs are worthy of equal protection -- not only are all men created equal, but all faiths are equal in the eyes of the law.
To those in a monotheistic paradigm, that secular assertion equates the validity of the opposition. To the fundamentalist, it says that blasphemy is equal to worship, that Satanism is equal to Christianity. The mere existence of the secular is a threat to the monotheistic extremist because it contains within it the heresy that any other position than his own is entitled to protection, respect, and serious consideration as an access to God.
To a mind that equates outsiders as enemies, violence is inevitable.