Question: "Is this dangerous?"

Answer: Well, yes. Hell yes.

As a motorcyclist I am frightened by these types of situations. Anything flying out of a truck can become a deadly missile and could kill someone riding behind.

Even if these bags were full of nothing but paper, a motorist behind might not know that and swerve to avoid it, causing an accident.

In one year I lost a windshield due to flying debris, and flattened two tires when I swerved to avoid something that had fallen off a truck.

When I was younger one of the families in our church lost their son (and his girlfriend) in a freak accident when a piece of re-bar fell off a truck, bounced off the roadway and impaled them on their motorcycle.

Anything not tied down is a danger and drivers should be ticketed and fined by law enforcement. Not tying down your load is a crime in most states.