Second hand markets help to keep the primary market propped up higher than it otherwise would be. If you can buy something and it retains resale value, then the initial purchase price is more worth it. Whether that balances out with supply/demand and price/sales numbers if there were no resalability is another question.

Second hand is different from pirating because the royalties have been paid. When it's sold to the second owner the status of having paid the royalties passes with it. With physical media the disk, tape, or reel and the license to use it privately are the same thing. Otherwise we'd need a system to keep track of who owns every disk, tape, or reel, and who owns the license to each and that's a sure fire way to get everyone to begin pirating.

Too bad, it's physical media, and people acting like "that's not what I mean" contributes to this whole idea that data is ephemeral and like it lives in the air or something. No, it all lives on physical media, on drives, somewhere. Just because Netflix streamed it to you doesn't mean that the movies files don't live somewhere on physical media. Yeah, you don't own it, it's just streaming, but the physical media it exists on still exists, you just don't have physical access to it (well, technically you do, it's just little chunks instead of the full film that live on your PC just long enough for the film to play).

Sorry, this grinds my gears because I think not being clear about physical media including things like hard drives and USB thumbsticks is what contributes to a general lack of understanding of how any of this fucking works and why corporations were able to get away with how they abused "licensing" for so long.