Islamic Extremism. Fact or fiction?

Islamic extremism is being talked about quite regularly on the news and other media outlets.  The idea of the United States pulling troops out of Iraq and Afghanistan has led to proponents of the war saying that Islamic Extremism will take the fight to the United States within the country's borders.  How real is that? Do you really think the war would be brought here if we don't stick it out and keep fighting?  Would Islamic extremists quit their fighting and live with us in peace?

I have my opinion, but am curious to hear others.

Thanks,

Adam