How is there a gun grabber analogy? Fencing is illegal, and immoral. The better analogy here is the “liar loans” in the mortgage crisis. You had borrowers lying on their paperwork, and mortgage companies who knew they were lying and didn’t care. Both parties are culpable.
It’s the gungrabber argument because you’re blaming the non-criminals for the actions of criminals. According to gungrabbers all sales of guns are bad because some guns wind up in the hands of bad guys and the gun store doesn’t know which ones those are and can’t prevent it, and according to you recyclers are bad because some of the people they’re purchasing from have stolen the copper and the doesn’t know which ones and can’t prevent it.
The recyclers DON’T know who’s got their copper illegally. They can make some guesses, but they don’t know. Not until somebody gets busted.