There are arguments for and against
It's a good question, Lee. On the one hand the violence adds to the realism of the game, perhaps but therein lies the problem, it breeds a more casual approach to the violence itself.
There is an argument that says the player will realise that it is only a game and it isn't really real and for a mature adult that's true, so why shouldn't those people be able to enjoy their preference? Why should we expect a "Nanny State" to shield them or prevent them playing these games?
But there are other categories of players, immature adults and kids, for example. The immature adult IS likely to become oblivious to the violence and maybe even accept it as a normal part of society today. Pour a few drinks down on a weekend and is there any surprise that gratuitous violence breaks out - not as bad as the deaths and "fountains of blood" that some games portray but random mindless violence none the less.
Kids are a different class altogether. They (or at least some of them) aren't old enough to separate the game from reality. When Tom hits Jerry over the head with a hammer, Jerry gets up and carries on running - what is a small child to make of this? If (s)he hits a sibling over the head, will they get up like Jerry? And therein lies the answer, I think. What (s)he is to think comes down to parental responsibility. It's obvious that Lee and his wife are always ready to coach or mentor their children, as I hope we were when our boys were growing up. But what about the other side of the coin (and put your "shock horror" look away, we've all seen it) where the parents give the child a TV or video game and just leave them to it? I believe in some quarters, this is referred to as "passive parenting". How is the child to form a value judgement on what is acceptable to society, if there is no guidance?
I'd like to think that all children had the care and attention that my parents gave to me and we did to our children, as do Lee and his wife but, sadly, I'm a realist and I know it isn't always the case. In that situation, yes, there is too much violence in video games.
There is an age classification system, like the cinema but unlike the cinema, where the classification is enforced at the box office, the video game industry is far more relaxed. If it were enforced, then that is the solution, when the classification says for a mature audience, that's fine, so long as the content is restricted to such mature audiences.
As I said at the beginning, there are arguments both ways. In all cases, except "passive parenting" it should be left up to the individual but then, how do you enforce it for the less concerned?