If you're able to, send the WB and, Rocksteady an e-mail or letter expressing this sentiment. It's true that buying used from gamestop will still get you the Catwoman code but that's only gamestop. It's a huge middle finger to every mom-n-pop shop trying to compete and an F-YOU to other retailers that offer game trading like Best Buy. Speaking of Best Buy, if you didn't preorder from them you can buy Robin for an additional $6.99 (rounding up to $7). If you didn't pre-order the game at all, but mearly bought the game on a whim from Gamestop you don't get any skins so while you're saving $10 on Catwoman, you're going to have to shell out $4.99($5) for the additional skins (and $7 for Robin).
Of course if you grab the game pre-owned from Best Buy, you'll probably get it for $55. Forgetting about Robin and the Skins, you would still need to give up $10 for Catwoman which has been heavily advertised for the last few months. It doesn't matter how little a role she plays as it's still single-player, story-mode content being withheld until the used player ponies up the extra cash. Unfortunately, I'm in the position where I can't connect to Xbox Live at all so even with a new copy, I'm locked out of bits of my own single-player mode.
I've sent a letter to the WB about this but doubt I'll see a reply since they're still going to make bank on this game anyway. I've already started to see that more than a few copies of the game were sold without the online pass! It probably won't be enough to make a significant number of people say 'No More' but there will be more now than there were before. It's this kind of nickle-and-dimming that's pushing me back into retro gaming, where you paid for a game once and knew you held in your hand a complete, finished product contained within a cartridge or, disc. Game companies make, and have made, more than enough money before these Online Passes became the norm. $10 is a drop in the bucket to these people and I'm done lining their pockets.