They like the market tragedy because they notice that morality plays in the west and they think of that as a western weakness. It is not *why* they think one way or another, it is just ammo in a propaganda war. It doesn't even matter if it is true.
Morality and weakness are synonyms. Cruelty and power are synonyms. They do not want to be moral, they want to be powerful. They see no way of accomplishing that by constructive means; they frankly would not know where to begin. But they can imagine accomplishing it by evil, by lack of scruple. They are aware that it is within their power to throw away all moral restraint. And they imagine if they could all just agree to do so, they'd be invincible.
They fundamentally believe that evil is more powerful that goodness, and that to secure power they only have to reach for greater acts of unscrupulous depravity. Then they will triumph over squeemish, weak, hypocritical westerners. They don't believe any of our professed regard for innocent human life. They think that is just blown smoke, the same as it would be if they said it.
They think our power resides in 2000 lb bombs, which if they had they'd drop indiscriminately on anyone they could reach. If we only drop them in certain places, they put that down to expense, to not having enough. They don't believe anyone can become and remain as powerful as they can see we are, without a cynicism as bottomless as their own.
Iraqi propaganda is consistently aimed at showing that westerners are "simpletons", made weak by our supposed morality, that that morality is at bottom just hypocritical, but that they are "morally" "stronger" in the sense of having stronger stomaches to engage in acts of the greatest possible depravity.
They relish the thought of torturing helpless enemies. It literally makes their male members stand erect. They think that is the secret of power and the route to worldly success. That is why they exhalt in such scenes, why a tape of the beheading of a Jewish reporter can circulate as a recruitment video. It is pornography to them.
Their psychology is perfectly understandable; they are the sort who love slasher movies and root for the killer. Not as escapist fantasy, but in broad daylight, in real life, on public streets. This isn't criticism or hyperbole. It is flat, realistic description.