It's silly that publishers think they should get money from secondhand sales. What other business gets profit from secondhand sales? You don't see your local furniture shop arguing that they should get money on that chair you sell, or electronics store saying they should get a cut from the sale of your old TV. Hell even the music business doesn't think they should get some of the money from selling your old CDs. Why do games publishers think they should?
The fact is they already make extra money from being able to sell DLC twice and online passes and the like. And a lot of gamers take money they made from trade-ins to buy new games so they make money on that too. It's stupid.