We spend a hell of a lot of time focusing on air planes but there is no way we can ever be fully secure. There isn’t a thing to stop them from attacking something like the DC metro or a crowded city bus.
Suppose a terrorist wanted to set off a bomb in the crowded line before security.
Now he/she/it doesn't need to pack a small enough bomb to get through the scanners and grope.
He/she/it can pack a carry on max sized suitcase solid with semtex and ball bearings.
TSA has thoughtfully assembled a target rich environment in a close confined space for them...