Can you really make that claim? Pending a true ruling on the matter (which given various laws and the lack of one thus far) blaming used games for anything seems roughly equivalent to blaming the magic games buying fairy for skipping out on buying a million copies of your game.
To go further game disc/carts at least are seen to have an inherent value and the ability to be resold which has existed basically since forever and saying if it didn't exist is not even a great thought exercise.
I do not buy new games*. Stores restock (place new orders) based on sales of new games, not on used games. Therefore the developers (or rather the publishers, which directly influence the developers) do not see any profit from me. The best they can do is make a good sequel, that maybe I will buy new.
To the actual games industry (unless you count GameStop as part of the industry, in which case, what's wrong with you?), I am no better than someone who downloaded the game. I am your proverbial magic fairy, and yes, there are THOUSANDS of us, just waiting for some idiot to buy a game new, sell it to GS for $4, and then buy it ourselves for <$20.
Also, what does inherent value have to do with anything? A sold digital copy (which, following your logic, doesn't exist) makes more for the publishers/developers than a used physical copy bought at the same time (say, after the game's print run is over).
*I have bought three new games, but in general, I only buy used.
Most publishers would be jumping for joy if the used games market disappeared overnight. Profit would skyrocket, though maybe not until after they revalued their products... I know I would pretty much quit gaming altogether, but for a few $4 downloads from GOG.