The only real danger violent videogames pose is that very young children might emulate it without understanding what they're doing. That certainly isn't specific to games, however, and has more to do with parental supervision than anything.
The truth is, for most people with normal brains, animated violence does not equate to real violence. A kid can "kill" his opponents all day long on a multiplayer game but that won't have the smallest fraction of the effect that seeing their parents hit each other would, or watching a bully beat someone up, or seeing a gang member pull out a gun. It's an entirely different experience. I've lopped off body parts in videogames but I still look away when someone breaks something in sports. I've seen people get mutilated in videogames without batting an eye but graphic stuff on the news will disturb me. It's just simply not the same thing, not even close to the same thing. I think it's insulting to imply that kids can't tell the difference between real and fiction.
As for the father and child playing a violent videogame together, at least they're spending time with one another. I remember a study that basically said that would be a net positive, that having shared fun together is a good thing even if it involves CoD--especially since the parent is there to guide the child and measure their reactions to see if anything is out of whack.
The FBI's profilers don't believe violent videogames create violent people and neither do I.
Edit: We also shouldn't forget that action-heavy games have a substantially positive effect on eye-sight and several portions of the brain. A person who plays videogames measures much better across several different cognitive tests than a person who does not.