If you can only sell the DVD but not the copy, then the original owner paid more for it, ends up with less value, and the new owner, if they wanted to sell it, would have the same issue. Further, you have to transfer a physical product, which at the prices of used DVDs makes very little sense and has a minor impact on the industry. Being able to sell a copy that costs nothing to make or ship is more damaging. It's not that they wish you couldn't sell your DVDs, too, but it's not as important a fight as digital copies.
I understand what you are saying, but understand in this case, I think they are having their own arguments used against them. So, while we might want to apply logic, we have to use the logic they've been using for years now. And, to be frank, that logic doesn't always make sense.
