Has that ever actually happened?
Plenty of instances of kids getting killed from having realistic looking toys, how many can you cite of police getting shot because they thought it was a toy?
Sounds like an utterly silly rationale to me.
This was based on information given during a street survival seminar several years ago. Since the information had been based on their sources in police intelligence divisions and street officers reporting on seizures, I decided to trust their word. You, of course, may have different sources.