It presents the same potential problems as carrying a fake hand grenade. It can unintentionally scare people, or intentionally scare people if used as a threat. There are other legal ways to send things from one place to another. He should have known better. He probably did know better.
I can't agree without knowing more. This man may have been unable to plan ahead further (ship the mine via UPS, for example)due to time demand, like the workshop is tomorrow or this afternoon.
Having logged way too many miles on commercial carriers in a dash for some meeting or other, I am totally sympathetic with the "consultant." Is there no secure area the mine could have been placed in so it could be retrieved as the man deplaned? That's what they used to do with guns before all this foolishness started.
Following 9-11 I switched to general aviation aircraft. The client pays whatever the added cost is, if he wants me there super-quick.