9/11 caused billions of dollars of economic damage, and we are still suffering the (stupid, self-imposed) effects - shuffling through airport security without our shoes, mass fingerprint surveillance, longer travel times, etc.
9/11 caused two wars, killing many thousands of soldiers, and maiming very many more, and those people now need expensive medical treatment and rehabilitation and benefits and etc.
The real damage wasn't self-imposed. It was imposed on us by poor leaders.
The solution lies within. The events of 9/11 were vivid, but in terms of GDP just a blip. It was the poor leadership that caused so much economic and human damage - spending hundreds of billions of dollars and tens of thousands of lives for basically no return at all.
We'll never have 100% control over foreign actors, but our government is an entirely different case. It exists by our whim alone. If instead we had spent just 1/100th of that money on better government accountability we'd be miles ahead of where we are today.
9/11 was a mild success but there is little reason to think it would work again simply because of reinforced cockpit doors.