Of course these days you could have a Raspberry Pi in a corner of the laptop case and the rest of it filled with whatever contraband, and still present a "working" computer to the security screener.

Nobody would seriously claim that airport security is an effective way of stopping determined people. It is a deterrent that works to catch thoroughly stupid people and to make smart people dwell on the anxiety of getting caught.

Nowadays your laptop would go through an X-ray machine with improved explosives detection.

Yep. I've never had to demonstrate that my devices are real at the security checkpoints getting into airports, I just put them in the trays and the X-ray scanners tell the agents that they're safe.

Now, dealing with the customs/pre-clearance checkpoints, that's another matter.