If North Korea or Iran could hold the world hostage with a threat of a mass-extinction-level event, they absolutely would. Similar for many terrorists of various stripes. Are you sure the control systems of whatever company ends up trying to bring back mass from space will be sufficiently resilient to hacking? I'm not. So, I worry.

And we're not even talking about "orbital" bombardment. We're talking about a continuous stream of material at well above escape velocity, whose delta-V is already paid for. Simply redirecting a few pieces of this stream would not be more telegraphed than any other attack. By the way, are you sure the control systems of the mine owners are resilient to coercion of their executives by "legitimate" terrestrial governments? I'm not. None of your reasons are effective.

The energies are substantially more than mining explosives, with wildly different properties as far as threat detection and mitigation. To put it charitably, that's a quite silly comparison.

Edit: now that I'm thinking about it, maybe the best mitigatiom would be to extrude all the mined material into some other very high surface area shape that can't survive reentry, no matter the mass, but can survive being accelerated for the trip home. Maybe a big long truss, with the engine at one end. And then also limit the payload size.