[nguoi]

I don't think that's a fair assertion. Even going in through the front doors with guns in their coats, the perpetrators of Columbine massacre used bags full of bombs.

>if they are looking to commit a public atrocity they'll...

Which gives everyone else a sooner notice to run away. This won't work for e.g. gang violence.

>Mandating clear backpacks is just as much security theater as is banning 4 oz liquid containers at the airport

Yes, they started that after someone actually tried to blow up a plane with bottles of explosive disguised as soft drinks.

[AnimalMuppet]

The bags full of bombs were to kill people after the shooters were dead. They weren't to get in the door. They got in the door by outgunning the security guard (one handgun vs two rifles in a gun battle, so the guard retreated).

[zepto]

How were they stopped if bottles were allowed?