2. Violent videogames are less violent (or disturbing) than other mediums.
Games like Dead Space and Manhunt sometimes got a lot of press for their violent imagery, and there was a lot of nasty stuff in those games. But they're peanuts compared to movies like Hostel, The Human Centipede, the Saw series, or The Last House on the Left.
For all their attempts at realistic graphics, games are still very far from the level of realism and shock you can get with live actors and movie props. Watch some of the dark scenes from Grand Theft Auto IV, then compare it to the graphic scenes of, say, I Spit on Your Grave. I'm not talking about some obscure homemade movies here. These aren't hidden cult movies. Some of these saw theatrical release and all of them are available on DVD and Netflix. Compared to these movies, your average Call of Duty gunfight looks like Sesame Street.
3. Videogames are regulated and restricted far better than other mediums
Movies have simplistic labels like R and PG-13 that will tell you what the approximate age level of the content is, but it won't tell you why. Music is even simpler, with nothing more than a parental advisory. Books have no content labels at all.
But in games we have many strata of warnings: Early Childhood, Everyone, Teen, Mature, and Adults Only. Not only that, but the labels will also tell you why the game is rated this way: Violence, sex, language, or drug use. No matter what sorts of content you're worried about, the ESRB labels give concerned parents the best possible picture of what the content is and who it's for.
Even better: Videogames have the best compliance record when it comes to adult ratings. Its far easier for a teen to buy a restricted movie or explicit music than for them to get a videogame rated M for Mature.
4. Videogame violence is normal.
Just like movies, just like books, and just like plays, videogames like to tell stories. Stories require conflict. Conflict is often resolved through violence. It's all part of how human beings tell stories, and it was millenia old before William Shakespeare ever got around to writing the first of his blood-soaked tales of murder, war, and rape.
5. Videogame violence is perfectly healthy.
Sports violence is real violence. People can and do get hurt all the time playing sports. Sports are far more dangerous than videogames. While people make a lot of scary talk about games "breeding hostility" or "increasing aggression", that's all it is: scary talk. Sure, people who play games sometimes get worked up. So do people who are stuck in traffic. It's nothing compared to the adrenaline-filled rage of your average football game. (And if we're talking about football in the European sense of the word, then feel free to compare videogame fandom with football fandom for incidents of riots and public vandalism.)
Surprisingly enough, human beings were not pacifists before Pong appeared in 1971. Like a lot of other mammals, we have a certain degree of innate aggression to cope with. We have a desire to be empowered, to protect, to compete, to overcome, and to test ourselves against obstacles. Historically, we've done a horrible job of finding ways to vent this excess energy in a way that didn't kill thousands of people.
Sports have been good for this. So are games. Hundreds of millions of people manage to play videogames every day without confusing fantasy with reality or allowing their virtual violence to leak into the real world. Depriving people of an outlet for their aggression will not stop them from feeling aggressive. It will just force them to find another way to express it. Blaming videogames for violence is like assuming the cat will stop tearing up the furniture if you take its scratching post away.
6. Videogame violence is fun.
No, really. Go shoot some aliens. Kill some bad ninjas. Or zombies. Or robots. It's all fun and nobody gets hurt.