These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Denzel Washington plays a cop that unflinchingly upholds the Constitution. Annette Benning plays a CIA Agent that compromises the law and makes mistakes, eventually getting killed for it. Bruce Willis plays a general that ignores the law to protect his country and its people. Guess who is portrayed as being in the right?
From a rather specific point of view, they're all right: Hub's steadfast belief in the law is what you'd expect from an FBI agent, but it utterly fails to work against the dedicated terrorists he's up against. Elise's attempts to sway and use people have their uses, as she's able to help identify several cells and gather needed intelligence, but the blowback from her offscreen operations set everything off. And Devereaux specifically argued against martial law, and specifically stated that he didn't want to do it, but he was ordered to and therefore he was doing it. He's not wrong to follow orders, and he has the best intentions in mind, but he does take it too far without realizing it.
Terrorism on U.S. soil may not have led to martial law, mass detention, torture by military personnel and use of helicopter gunships in urban areas, but the subsequent counter-insurgency campaign in Iraq used exactly these tactics.
Not as unusual as one thinks. Mass detention certainly did not happen (even the large numbers of Saddam's military captured were more or less released after Baghdad), helicopter gunships were used in urban areas as far back as Korea (and also in Indochina, Grenada, Panama, Yugoslavia, and Afghanistan) and indeed were expected to be utilized in the WWII invasion of Japan. So this is nowhere near as unprecedented as it seems at first... which says something VERY unpleasant about the military. War Is Hell indeed.
This trope is also inverted of sort in that the tipping point is a bombing of an FBI building that leaves 500 officers dead. The movie treats it as the most horrific terrorist act that could ever happen in the US. As it turns out, real life had a scarier idea...
Though part of why that attack was so devastating was that with the FBI office destroyed, their capability to respond to additional attacks was severely weakened.
It's also possible that if continuous terrorist attacks occurred, martial law and the detention without charge of "suspicious" people would have been utilized. All of the film's elements were done, just not in New York City, but overseas.
Post 9-11, FOX itself lampshades this by marketing the movie as "Eerily prescient of the 9/11 attack and their aftermath" on the backcopy of the blu-ray DVD edition.
"I'm not arguing that The Siege is a deliberately offensive movie. It's not that brainy. In its clumsy way, it throws in comments now and then to show it knows the difference between Arab terrorists and American citizens. But the prejudicial attitudes embodied in the film are insidious, like the anti-Semitism that infected fiction and journalism in the 1930s—not just in Germany, but in Britain and America."