The islamist agenda is to spread islam and sharia law around the world, and they are using the openness of western societies to further the downfall of western culture. To understand muslim expansionism, people need to look back to the spanish conquest of the new world. There are two avenues of conquest, military and religious/cultural.
Even as the spanish military ran over the native people of central and south america, the missionaries moved in to build "cultural centers" or missions where they could teach christianity and minister to the needs of those same native people. It was a brutal but effective tactic which all but destroyed the traditional cultures in only a few generations. The missionaries incorporated the religious sites and stories of the native people into christianity, and those blended religious themes are still apparent in celebrations like the day of the dead in mexico.
islam used the same techniques in the past conquests of lands from malaysia to bulgaria. The ottoman empire was almost as brutal and oppressive to the christians of europe as the spanish empire was toward the native peoples of america. And the techniques used had many similarities.
In the 21st century, islamists will use the democratic traditions of the west to try to impose a new cultural imperialsm. In the ground zero mosque debate, we see the themes played out clearly. On the site of the mulism's greatest military victory against the west, (or, to appease the islamic apologists, a few hundred yards from the site) the muslims are seeking to build a "cultural center." To muslims, and to westerners not blinded by ideology, the meaning is clear. Just as the spanish built missions of mark their cultural dominance over the native americans, and as muslims converted christian, buddhist or hindu religious sites into mosques, the new islamic expansion is negating the symbols of america and the west.
People want to think that hitler and mussolini used violence to impose totalitarianism in europe. But the democratic process is open to subversion by a militant minority willing to use the principles of tolerance and openness for their own ends.
As I have said before, the threat of islamic expansion is much greater in europe than in america. But every victory for islamists is a defeat for the west. The identity politics of the left, seen in the declaration of the obama administration that there is no "war on terror", weakens the cultural values of western democracies and opens the door to cultural conquest.