You could be riding with a bomb, drugs, weaponry, etc, at any time and have no idea.
Well bombs doubtful, weapons yes (and what's it matter if they are in the hold?) and drugs for sure, though most are transported by truck like everything else people buy in the US - but if you're on a plane in the US it's a good bet that at least one of your fellow passengers packed a gun, and a few others have some contraband on them. The odds are over 90% that if you have any large bills on you, $50s, $100s, that they will test positive for drugs, so for sure the plane you're on has some.
It's security theatre, it's not really security but it looks a lot like it. Most people have NO clue, well you could have stopped there pretty much. But what they have no idea what's its like is what is required for real security, and even more-so, they sure are not going to want to PAY for what real security would cost (money and freedom, but mostly it would be the cost that gets them upset). I watch ships come and go from the Bay all the time, HUGE SHIPS (really, if you're landlocked, it's hard to imagine how large the super-tankers and huge containerized cargo and cruise ships really are) and they are not inspected before coming into the Bay, Then they are parked right downtown, or at a major port, or at an oil refinery.