Just because EA eats the cost of additional server usage after whatever cost was factored into buying the original game doesn't mean that you can just pass it around to whomever and every should enjoy it equally. The cost of running a server is not a set cost like the cost of producing the game that is on the disc. Servers are updated, optimized, maintenanced and constantly on providing a centralized place for all users to connect. That's not including whatever additional content that may come with a online connection, like updated rosters, gameplay updates, tournaments, DLC, patches, etc etc.
The game disc is your to do with as you please, but the online portion of the game is not on the disc. You want to resell your game? then fine, you still have the option to come back at anytime since your pass has already been activated, but just because you left the game early doesn't mean the next person off the street can buy your ticket and assume your identity and take your place. That person needs to check in at the front desk and get their own ticket using their own identity.
and if someone bought the game for $5 less than new because they wanted to save $5, then it's gonna cost them $5 more than if they had just bought it new to play online. Maybe they get lucky and the first user didn't use their online code, but really, unless you saving a whole bunch of money, why buy someone elses second hand stuff when a new one barely cost more?