What they don't understand is that the backpacks aren't part of a program to protect them from some bad guy.
The backpacks are a part of a program that sees them as the bad guy. Every last one of them is a potential criminal. The backpacks allow authorities to see what they are carrying. It's what they asked for. A system that disarms everyone and then relies on the government for protection.
It's the same policy as at the airports and an extension of the same thinking. Every person that gets on the plane, from the toddler to the elderly nun, is considered a potential threat and is sheared, scanned, profiled, and probed.
In this brave new world, there are only the watchers and the watched.
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
--The 4th Amendment to the U.S. Constitution