The United States is still one of the most Christian countries in the world. I am not at all sure that you are correct when you say than militant Islamicists are not representative of the true Islam. There are many scholars who would not agree with you.
As a Catholic, I might not disagree with them as vociferously as you think. Islam's very materialistic -- heaven is a seraglio -- bent does indeed result in some unfortunate errors of ideology and ensuing violent spread of Islam.
While we may have plenty of Christian folk in the United States, ours is a top-down Culture of Death and "Western Materialism" about which there is nothing particularly Christian IMHO.
It's unfortunate this tragedy comes on the heels of Bush's confirming with federal funding that we no longer perceive all men as having been CREATED EQUAL.
I warned folks that would tear it for me ... confirm in no uncertain terms -- even those backed up by some personal interpretation of Twisted Scripture -- that we have abandoned entirely the self-evident and patently Christian truths on which this nation was founded.