The US military has spent billions of dollars developing stealth aircraft which are invisible to radar so they can mount surprise attacks on adversaries, but it seems they should have saved their money and bought a fleet of airliners because they appear to be far more effective.
On 9/11 the world's only military superpower was apparently oblivious to the location of rogue airliners in it's airspace for more than an hour, and military commanders were left totally perplexed on how to deal with the situation of hijackers using these planes as flying bombs. This confusion resulted in fighter jets staying on the ground whilst the hierarchy fully assessed what was going on, and this total lack of cohesion ultimately led to the loss of nearly 3000 lives.
All that was required to overcome America's military might on 9/11 were 19 hijackers on 4 airliners.
Does this sound plausible to you?
It's what you're expected to believe.