I posted a rather long-winded opinion on this some time back, about socialists. I thought I'd do the same thing for citizens of Arab nations, only shorter. Here goes:
They're told to.
Yep, that's it.
Oh, and anyone who dissents gets his head sawed off.
You'd think people who treasure their right to disagree as much as Americans do would understand this. But in case not, let me spell it out. In the vast majority of Arab societies, you get the government's line. Your parents, aunts, uncles, grandparents, etc., repeat the line, or get disappeared. It's on TV, the radio, movie screens. It's in the textbooks you read from kindergarten to university graduation. It pours from the mouth of every teacher, every preacher, every friend.
It's truth, because you want to survive. It HAS to be truth, because you never hear anything else, except from traitors, and then only briefly.