What is worse on that behavior ?
Your visitor's won't pickup their droped weapon.
And you can't use or sell them.
The only thing i can see not to smelt them is when you hope the visitor might join you after he got rescued, and the weapon isn't that bad.
But then you still can adjust your smelt bill not to smelt good+ weapons, and just create single smelt bills for good biocoded weapon you don't have an owner anymore in sight.