Not Islam, but the ultra-reactionary form of Islam known as Wahhabism is behind the insanity. Its roots go back to the nineteenth century, and it is the dominant ideology in Saudi Arabia, which results the misogny and the rest of it that everyone knows about there. If a million Mormons were migrating onto the Continent, people might be bored, but not scared. Why? Because there is nothing as severe, violent, and punishing as Wahhabism associated with it.
This article is a good account of ISIL along the lines of the long
Atlantic article that Bill linked to.
As for the passport and Syria, it is definitely good to be cautious about what it all means, but the
Guardian and others are reporting that the fingerprints of the terrorist where the passport was found match those of someone entering through Greece in October. Not conclusive, and maybe it's a hoax to freak people out, but . . .