TSA isn’t even the one making the airport feel like a militarized zone. Most agents aren’t allowed to be armed nor have any more power than regular citizens. They are the same as a bouncer of a club. I don’t know about the USA but in most countries it’s either the police or the military providing the protection.

Airport and flying safety has improved significantly over the past few years. Plane hijackings used to be way more common pre 9-11. The reason why 9-11 worked was because there was a protocol in place on how to deal with hijackings. And that was to follow the demands of the hijackers. Because this would safe the most lives.

Today the protocol has changed. Pilots will never open the cockpit door, no matter what the hijackers are threatening or actually doing to passengers. And ironically this also means that the TSA does a better job than most assume. Because the main priority is to ensure hijackers can’t get into the cockpit. Bringing any equipment onto a plane that could help tearing down that door is almost certainly going to be detected by the screening.