Seaman, I think we shall just have to agree to disagree. I see no reason that a person intent on an armed or strong-arm robbery would stop and get down on the ground just because you or I said so. This scenario reminds me in some ways of the idea that bad guys will observe signs and laws prohibiting them from having guns, in that their lack of respect for rules is what makes them bad guys to begin with. I would have zero expectation of compliance if I gave such an order without drawing. Perhaps you have a more authoritative voice than do I.
I am trying to imagine a situation where I would feel justified in ordering a stranger to the ground but not justified in clearing leather, and I honestly can't come up with one.
Plus, as MLeake said more eloquently and accurately than I, your policy loses you the very real opportunity to end the threat by producing a firearm but not firing.