but this movie was done after a major attack on the world trade center in the 1990s by islamists.
i mostly will not be able to answer your reply, since marissa mayer hacked my email, no notification

No one really thought how people would react to a large terrorist attack on US soil. Every other movie that attempted to do this, always failed with unrealistic heroes/reactions and ultimately bad cliche in movies.
And probably you were born on the 90's or late 80's and have little recollection on living in a world pre-9/11. It was better then. People had more freedom then than we have now. You could go through security check points under 5 min, you could trust people more. Anyway. many things shown in the movie were spot on with 9/11. About AMERICANS not arabs.
The american reaction it's what it is interesting about the movie.

Hollywood was preparing the American psyche so to accept the future coming staged terrorist attacks and you know who owns Hollywood don't you!
English is not my native language.
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The way the US (in the movie) suppressed civil rights in the name of public safety. Which was a mirror and foreboding to the Patriot Act IRL. Torture which was somewhat of a debate a few years ago.

The Siege was somewhat more adult. Even though it dealt with the issue, the actual terrorists in the movie were also stock villains. The main terrorist, Samir, was acting all angry muslim, in a stereotypical Hollywood fashion, so I felt the terrorists were stock characters. The story itself dealt with the issue more though for sure.

Probably because it dealt with the issue in a more adult manor. "True Lies" and "Executive Decision" (I enjoy both movies) just used Islamic Terrorists as stock bad guys; like the Nazis in "Indiana Jones," the Empire in "Star Wars" or generic gang bangers in many urban cop thrillers.
This film actually dealt with the idea that while Islamic terrorists are a threat there are plenty of Muslims who are proud American citizens; who might find it degrading to be lumped in with (arrested/detained/tortured along side of) the very people who they came to the USA to get away from in the first place.
Also it dealt with the issue of torture before it was such a hot button political issue.