I think the point that you are missing, and which Maineman was very clearly stating, is that the ideology in question wasn't prevalent in the country that we attacked. So, if you believe the war was against an ideology, the question then becomes "why attack Iraq?" I think millions of Americans would be surprised to find it was merely to depose a dictator (one of many around the world I might add) and establish a presence in Iraq. Especially since establishing a presence in Iraq has increased the appeal of the said ideology.
By the way, you never clarified for me why Iraq is a significantly better place for a US military presence than Djibouti, Qatar, Bahrain, Kuwait, etc. (except of course, that our soldiers happen to be getting a lot of practice right about now).