Why exactly are they against used games? Don't they still get profits off them?
no, and neither should they.
lets put it this way; i buy a toaster, use it for 3 years and then sell it in a garage sale. the toaster is the "game" and the garage is the "used game store"
How its always been is that when i buy the toaster, it belongs to me and i can do what ever i want with it, such as sell it to a neighbor.
In recent times toaster manufacturerers are trying to come up with ways to prevent their profits from coming to a plateau
(because when that happens to a corporation, its stock holders begin to sell their stocks in large quantities with the assumption that those stocks are at their most valuable point)
conventional ways to increase profits is by raising the margin of profit, which is to say charge a larger % of money for the same product, but that causes a decline in sales. Also they can't increase a % based profit by producing and selling larger quantities of copies because in the eyes stock value the margin will not increase.
So they look for ways to get "add on" sales. An example of an add on in regards of the gaming industry is DLC, however generally DLC still requires production so they can only increase their margin of profit by either charging A level price for D level Production, or by with holding content that was already going to be in the game and selling it immediately after release as day one DLC.
Now the most recent "add on" is their attempt to either promote some sort of "developer's tax" on used game sales (hence getting paid twice for selling one physical copy), or simply by killing the used game market completely. Which would raise their margins by destroying and consuming a whole sub market, forcing used game consumers to pay full price for a game they ultimately did not think was a high enough quality game to pay full price for.
They justify this by saying that used games cause them to loose a sale, but thats nonsense, since the game that is being bought used was bought by the previous owner.
so essentially the toaster manufacturers want to show up to my garage sale and demand a cut of my profits i made selling my toaster to my neighbor.