Who actually got hurt? Let's see...

Okay, so, the online pass will cost you $10 if you buy a used game.

When you buy a new game for $60 and then sell it to Gamestop.

Assuming Gamestop normally would pay you $30 and resell it for $50, but they won't foot the bill for online pass and the buyer won't want to shell out an extra $10 neither.

So, instead, Gamestop will buy that game you could have sold them for $30 for only $20, and then sell it to the buyer for $40, who then pay another $10 for the online pass. Neither of them lose anything.

EA made an extra $10 from the online pass.

But wait... who actually lose out on this? The person who bought it new.

It's not Gamestop. It's not that horrible buyer who bought your used game. IT IS YOU who support EA in the first place by buying new.

Not exactly. Anyone who sells a game, whether it is a new game or a used game, "loses" when they sell it, when compared to what was before. When I buy a game new, I basically pay $50 plus $10 for the online. then (in theory) get back from Gamestop $20. But if I buy used, it's the same thing, I pay $40 plus $10 for the online, and if I sell the game I also lose these $10 I spent on online.

Since I don't subscribe to the "everything should be free even if it makes the developer lose money and eventually shut down " school of thought (in this case footing the bill for continuous online support), I rather agree with the logic behind EA's move. The only down side (at the idea level, not the application itself) is that as a new game buyer it makes you pay for something you may not use in the game (the online) - a solution to that would be to make online optional for the new game buyer as well, meaning they would pay $50 when buying the game and $10 if they want an online pass.

So, then, where does the extra $10 come from, if neither Gamestop or used-buyer foot the bill?

Well, we don't know how Gamestop will handle it on a regular basis yet. Gamestop may ignore the online fee, and continue to charge the same prices, in which case the used buyer gets screwed. (Essentially, with an edge card, they'd save a net of 50 cents buying used on a $60 game.) If Gamestop does lower what they pay (and charge) by $10, then the loser is the person who trades in games. It wouldn't matter if they bought it new or used, they're going to get less for their game. (And it'll be all that faster to when Gamestop pays you a quarter for it.) However, my theory is that Gamestop will actually take a bit of it, since paying someone $20 for a $60 game that came out less than a week ago is laughably bad, so I'm guessing that they'd probably go from $30 to $25 (still pathetic, mind you), and drop the price from $55 to $45. Conversely, I can see GS just dropping $5 across the board too, making the price for a used game the "same" as a new game with the pass, but allowing GS more profit, and pushing their edge card again for savings.

TL;DR version: I don't think 1 person will bear the brunt of it.

I remember there was an issue though with ME2 where GS employees didn't tell used game buyers about the Cerberus Network thing, and people got pissed off about it, so I doubt selling games at $50 $10 will work well for them. If they try to be sleazy and don't tell the consumers, they'll piss people off. If they do, the consumer will think "Hmm, I can pay $60 for a used game or $60 for a new game, easy choice". This is assuming a consumer wants the game when it is relatively new of course. 

In the end though, I don't know if this idea will work. If it does, great, keep doing it. if it doesn't, they better drop it fast. Of course, what one can mean but 'if this idea will work' is totally relative anyways. Personally, I just think there should be some sort of law requiring retailers to give publishers a certain cut from used game sales. I think that would be the cleanest and fairest solution, but things don't usually work out so easily.

... How do we know Gamestop will give us less for the game?

I buy all my game's new... I'm taking a 45 minute drive tomorrow just to pick up a new copy of the Heavy Rain Collector's Edition because none are available in my area. I also don't trade in games. So I'm one of the people who are in a win win situation, I support the developer I like and I don't lose $10 : ).

Do you think Gamestop is just going to eat that $10?  No, they are going to pass that on to the consumer.  They are going to do everything in their power to keep their margins the same.

so how do you know it won't be the same to the guy who sells his game and -10 the the guy who purchases a used game?  or maybe 5 and 5.  or how about gamestop loses some margins?...like a 3,3, and 4?  this OP is making an awful lot of assumptions with nothing to back them.

..and why is everyone's butt so hurt but this?  as far as i'm concerned this is a good thing.

How is Gamestop going to move inventory if they try and take the $10 from the guy buying the game?  A used game is $55, and pass is $10.  So you end up paying $65 for a used game?  I don't think so.  Split 5 and 5 that still makes a complete used game $60, and no one is going to buy that either.  This policy will decrease the value of a used game.

In the real world, games that have this policy in place are not going to drop the full $10 though.  If multiplayer is only important to say, 50% of the people who buy that game, then the used value of that game is probably only going to be $5 less then what it normally would be.  So in the end, I think there are probably three losers here.  Those who buy games new and then trade them in, those who buy multiplayer games used or rent them, and the publishers in the long run will likely see decreased new sales due to the weakening of the used market.