They were the ones with the device, they were the ones that typed in the code. [...] and you give them one set on fire and they light the house on fire themselves.
I have no idea how some people can believe the words they say. Literally the entire point of a duress code is that the attacker doesn't know that it's a duress code – that it looks indistinguishable from a normal password. In your example, the key is physically on fire. A duress code is "oops, I gave you the key that activates a hidden mechanism to burn my house down. Guess you're the ones who destroyed it lol."
To say "well your honor, I intentionally tricked someone into destroying the evidence for me" would not hold up in court is an understatement.
I'm not trying to be condescending, genuinely making sure because your analogy is so far-off: you are familiar with what a duress password is, right?