Yes it is. Don't forget roughly 3,000 civilians who died on 9-11. It's not all just travel inconvenience.
First of all: I don't want to downsize how horrible the 9-11 attacks were the slightest bit. They were horrible. No discussion there. And any reasonable actions that can be taken to prevent that from happening again should obviously be taken.
But you've got to put things in perspective.
Every year, about 435,000 Americans die because of smoking. 111,909 because of overweight and obesity. 85,000 because of alcohol abuse. 75,000 because of infectious diseases. 55,000 because of toxins. 43,000 in motor vehicle collisions. 16,586 commit suicide. 10,801 people get murdered with firearms. 776 die in accidents with firearms. 20,000 die because of sexually transmitted infections. 17,000 die of drug abuse every year. And 90 get hit by lightning. And how many people got killed by foreign attacks on American soil? 3,000 in the last 68 years (since Pearl Harbor). So that's an average of less than 50 a year in the last 68 years. So purely statistically speaking, your chances of getting killed by a foreign terrorist in the USA are extremely low. Not even half as high as getting killed by lightning.
Which, once again, doesn't mean that America doesn't have has the right to do whatever they can to prevent something like 9-11 from happening again.
But how are things going with the "War on tobacco"? Any progress yet in "The war on obesity"? How about the "The war on alcohol"? Any news on "The war on firearms"? Or that "War on lightning"?
And yet, the "War on terror" was important enough to invade two countries and pretty much abolish the right to personal privacy. It's mostly mass hysteria and stimulated paranoia that's shamelessly being exploited. And you can never have any guarantees anyway. The attacks in London and Madrid weren't even on airplanes or airports.