I know this post is going to be very generalizing, but looking as an outsider at the US, and what shapes the opinion in the US I see the following three factors. Please correct me if I'm wrong, and I hope I am.
1) Cultural ignorance
Speaking to Americans (not the people on this forum of course

) I get the strong impression that a large part of the country is completely ignorant about the rest of the world. And that goes for the lower class, middle class as well as those who call themselves intellectuals. And that those who do have that knowledge have obtained it through their own efforts, not by virtue of the educational system.
If you want to understand the Middle East you have to dig into its history, all the way down to biblical times. You have to understand geography, the cultures and the religions.
2) A strong desire to see everything black and white
Americans like to see the world in a framework consisting of good and bad. It is a recurrent theme in movies, news, and politics. The good guy versus the bad guy, the allegiance of justice and democracy versus the axis of evil. In a conflict, someone must be good, and consequently someone must be evil.
In the Middle East there is no black and white, just a whole lot different shades of gray.
3) A biased media.
In contrast to the previous post I don't think the US media is unbiased. I admit that I only get the major channels here CNN, Fox NBC and not the smaller channels, but comparing them to other media, like BBC, SKY, TV5, ZDF they do have a bias. And that bias is not exactly in favor of non-western nations.
So you have a lot of people which are extremely opinionated on a subject, without having the necessary background information to aid that decision, and with a biased media system as only input.