Co-op is out for blood. It's target: singleplayer campaigns. If we don't make an effort to protect our story modes, and keep co-op out of their natural habitat, we might see them become extinct.

Truly though, this is a new trend that I really don't like. As of recent years developers have made efforts to make their singleplayer campaigns also work just fine when played with some buddies. Sometimes, it does work just fine (see Halo, or Gears of War), but most of the time I find myself wishing that my singleplayer campaign would (shockingly enough) be designed for just one player. If a co-op campaign is added on top of a solo mode (like in Splinter Cell: Chaos Theory), then that's icing on the cake, but I hate to see developers go out of their way to craft a singleplayer mode that just doesn't end up being very fun to play alone.

Prime example: Resident Evil 5. Capcom took any feelings of isolation, and fear (which you'd expect in a survival horror game) and tore it to shreds by including a sidekick that is with you at all times. It's sad to see the developers effectively destroy their series' identity simply for the sake of adding in that co-op mechanic. Playing with a friend is always fun, but if it ruins the atmosphere of a game, it's not worth it.

Another terrible thing about singleplayer, and co-op campaigns being one in the same is the experience you get when you don't have a buddy around. Developers still have yet to master friendly AI that can aid you in a significant way, so usually players will have to keep track of their AI partner who was designed to be player-controlled in the first place.

The co-op-designed singleplayer campaign, at this point in time, doesn't work well enough to be as commonly implemented as it has. Some developers go out of their way simply to add in the co-op mechanic, others hastily throw it together even if it doesn't really fit the game, and very few can actually pull it off. So please, developers, think about the poor singleplayer campaigns you've been killing and ask yourself: what did they ever do to you?