They showed that they don't negotiate, so doing a terrorist siege would lead to nothing.
From Daniel Greenfield's "Where the Black Flags Fly"
If you reward violence with concessions, there's no reason for it to ever stop. And if you don't, what else is there to do?
When life is worthless, everyone has a gun and a grudge, it's easier to kill than not to kill.
It's best to understand that we are not dealing with a moral code that looks anything like our own. The nastier qualities of human nature, deceit, violence and greed, are practically virtues. Especially if they are directed at the right targets.
There's a reason that Islam was born here. There's a reason that it still thrives here largely in its unaltered form.