Copper, Brass and Stainless Steel are all Metal Alloys.
Some Copper Alloys are Fine to be used around some Foods (non-acidic) or in Water Lines. Some are Not. The Hard part is Knowing which Alloy is Which? And what you are Actually Holding in your Hand?
That is what makes Stainless Steel very Appealing to people. Because almost Any Stainless Steel Alloy is going to be Fine.
For anything that comes in contact with e-Liquids, I would Strongly suggest that a Person chooses Stainless Steel.
Is there any real evidence at all that e juice + copper or brass is in any way harmful?
Or is all this fear based on anecdotal half-data?
I'm not aware of any data on e juice and copper.
I don't think anyone really knows what your stock copper water lines are made up of...or the lines to the coffee machine in your favorite restaurant.
Most copper lines are manufactured........in China!
Be sure your trust of contractors and builders aren't misplaced.
Before you fear something ask for real data.