We can argue a lot about whether buying games used is ethical or responsible, but what's going on here is different. This isn't about customers at all. When a game gets sold used the retailer takes all the revenue from that. The publisher and developer say "That's not fair, we made that. We deserve a cut." Since there's no legal ground for them to claim that cut and there's nothing they can offer in return for it (I'm surmising this from the fact that, to my knowledge, no publisher or developer has a profit-sharing deal with a used game retailer) they've just been living with this "loss" until now.
This plan is a way to forcibly take that cut from the resalers. Note that I didn't say customers. That's because the resalers are going to have this conversation with their customers:
Gamestop: Buy it used, it's much cheaper.
Customer: Only by $5, and then I have to buy the online pass, which costs $10, so I'm out $5 if I go with a used one.
GS: Ok ok, our used games will be $15 off now.
So basically the resaler accepts that used games re now devalued by about $10 and reprices accordingly, because used sales are still more profitable than new sales (though less so now) and sometimes the alternative ill be not making a sale at all, new or used.
It's a little more complicated than that, because this will also influence the trade-ins that resalers pay out, and some people will just decide they don't care about the online pass, but hopefully I've demonstrated the basic idea here, that this is mainly about EA forcibly taking a cut from resalers, and counting on them to eat the cost.