This argument seems to focus a lot on the current trend of Garglespunkweewee, and I agree with it. Games like Call of Duty started as single player games. The current modern re-hash of them also was noted for it's single player campaign. However, after that, people started excusing the poor campaign because they spent most of their time in multiplayer. This is unexcusable, because every commercial, and every previous iteration was primarily a single player experience. Multiplayer should be the thing you do after you beat the game, not the reason you purchase it. If they want to make a multiplayer-centric Call of Duty series, it should be marketed like the Unreal Tournament series: a series that contains single player, but is mostly meant to be played online.
Now for Battlefield 3, I don't know what to think. As far as I know, the Battlefield series was never single player, or at least in the sense that COD was at the time. The fact that BF3 has a singleplayer campaign shows they were too busy trying to copy COD, rather than make the best damn multiplayer shooter they could. This makes little sense, because if people only play COD for the multiplayer, then wasting resources on something no one is looking for is just idiocy. That's EA for you I guess.
So to answer the implied question in the poll, yes, games need to stand on their singleplayer. This of course doesn't apply to games like Team Fortress 2, but even if it had to, at least the singleplayer mode is identical to the multiplayer mode. No mechanics are changed, and the player still has to handle the same game, even if it's stupid by comparison. The same can't be said for COD and BF3.