I think that once you already can't afford to buy new games from the publishers, then even pirating the rest is less harmful than selling and buying used ones.
The result is almost the same, you get to play a few of your games without rewarding the artists, but at least in that case, instead of giving part of your gaming budget to Gamestop, you are keeping it in your pocket, for the possibility of spending it on other new games later.
Used games are more like those old-fashined "warez" piracy sites, and disc-bootlegging, that people had to pay for, not even just skipping the publishing industry, but draining away potential business from it.