"For the vast majority of players, even those who regularly play and enjoy violent games, violence was not a plus," study lead author Andrew Przybylski, a Rochester graduate student, said in a news release issued by the university.

The plus isn’t for the player, necessarily. But what violence does do is communicate clearly.

"Kill or be killed" is a primal and simple way to explain to a Player their relationship between themselves and the other objects in the world. And their first goal will be to find out just how the game intends to let them do that.

It’s certainly not the only way, nor is it going to be popular with a lot of demographics, but everyone gets it, whether they like it or not. Violence avoids the need to try and create a context for why I might you might want to match three of a similar object together.  Gore shows you that you’ve done the right thing, because if something is exploding into a shower of blood, then you probably did what you were supposed to do.

The research, consisting of two online surveys and four experimental studies, found that overcoming hurdles, getting a feeling of accomplishment and having multiple choices for strategy and action appealed the most to seasoned video gamers and novices alike.

There are reasons to not use violence and gore as your basic toolset, but the above quote confuses cause and effect. Games use violence because it communicates accomplishment and helps you overcome hurdles, not because it feels good to be violent.

As games become more socialized violence will probably become a tool favored more by cooperative games (us vs. them) than head to head play (you vs. me).  After all, it’s far more socially acceptable to shoot a computer generated monster than your best friend.