Yeah. The "security theater" absolutely does play its part in stopping attacks. Without it, airplanes would be an extremely easy target for any nutjob to commit mass murder in. They wouldn't even necessarily need a bomb, anything that can cause a big enough fire mid-flight could be potentially catastrophic. Over past few decades many airliners have crashed because out of control fire in the cabin / cargo hold. I really don't want it to be easy for any random person to cause such fire.

Trains are a much easier target in most countries. Generally only the high-speed / cross border ones have any security at all. Until maybe 10 years ago you didn't even really need a ticket to get access to one (now ticket barriers are common).

There's a pretty strong trend in that timeline of two types of "bombings":

(1) Bombings in which the bomb is supplied by someone who isn't flying on the plane;

(2) Failed hijackings in which there was no intent to bomb the plane, but a bomb accidentally went off.