Everywhere you look nowadays, Islam is used (and misused) as a political force. Some Muslims employ it as a call to action; many in the West (and elsewhere) perceive it as an "other" demanding containment and exclusion. As a Turk, I feel both sides of this debate directly.
The reason that Islam seems like a religion of the "other" to Western eyes is that the West has witnessed a systematic de-institutionalization of religion. It is not religion that disappeared from modern Western life, of course, but rather the claims that religious institutions can make on individual behavior. Religion in the modern world is a much more personal and spiritual experience than ever before.
Yet a process of de-institutionalization of religious experience is also taking place within Islam. Politicization of Islam is displacing the authority of Islam's religious classes, the ulema . As in the West, Islamic religious experience is becoming more personal. Interpretation of religious texts by individual Muslims, including political militants, intellectuals and women, is one result. Another is the vulgarization of religious knowledge, with the Koran's teachings abused and taken out of context to support political ends.
Who now decides what is legitimate and what is illicit in Islam? Who has the authority to interpret religious texts? Who can issue a "fatwa" or declare "jihad"? Nowadays, activism and terrorism provide, or rather impose, a new source of legitimacy. So lay people decide what Islam does and does not mean, without the authority of religious schools and specialized training.