Earlier quoted context omitted.
Stainless in (or near) contact with copper with moisture between them forms a battery, which will corrode them. Metals in a plumbing (i.e. wet) system need to be either isolated from each other or be galvanically compatible. This applies to roofing, too. Nail the flashing down with galvanically compatible nails, or you'll find the flashing all comes loose after a couple years.
> Stainless in (or near) contact with copper with moisture between them forms a battery, which will corrode them. Not really? A battery has two paired half reactions. Something gets oxidized, something gets reduced, and electrons flow through the conductive bits. So if you have some metallic zinc, and you have some copper ions, and you have some metallic copper, and you have electrical contact, zinc will be oxidized,…
You'll also find the same if you google for copper and stainless galvanic compatibility.