It all depends on the medium and the context. In general my view is only the minimum to achieve the correct effect is needed and anything beyond is gratuitous.
Clearly, certain stuff falls into a grey area. For example Torture Porn movies. Do I like 'em? No. But I accept if you're going to make one for those that like it (you sickos know who you are!) then the whole point is to be gratuitous.
In games I think it's also a grey area since, to be blunt, in most cases we're talking about fake reality for fun or to appeal on more basic levels. I don't care what anyone says Modern Warfare 2, for example, isn't in anyway a combat simulator or should be seen as providing any insight at all on combat. It's a virtual game of cowboys and indians with soldiers instead of cowboys, plain and simple and appeals in exactly the same fashion.
Therefore, given the relative lack of artistic merit, do I think having a lot of violence in a game is gratuitous? Probably, but as with the Torture Porn in a game that's kind of the point.
In films like The Thin Red Line or Saving Private Ryan (which is pretty flawed as a film IMHO compared to the former, but anywho...) the realstic depiction of combat violence and <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-fareast-language:EN-US;} @page Section1 {size:612.0pt 792.0pt; margin:72.0pt 90.0pt 72.0pt 90.0pt; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> psychological violence is justified and I'd argue necessary to convery the true extent of a very extreme element of our real, actual society.
In games, for the most part if we're honest it's for fun and kicks. We have violent headshots as a visual reward for pulling of the skillful shot, and to deliver a higher sense of reward for the player, for example. Certainly it couldn't be further from the intent, in say a war film, to horrify with the terrible damage and suddeness of someone, a friend, a fellow soldier, being shot in the head.
I believe a huge element of the disconnect between violence depiction in games, and how the media respond to it, and violence depiction in films, is down to a misunderstanding regarding the nature of the intent in each medium and how it should be understood.
Saying that, I've never liked the real world combat settings (WW2 or Modern) in shooters. I'm always aware that in truth we're taking very real, impactful events and using them as a setting to for virtual cowboys and indians, and I'm never sure that there is enough justification to to do vs simply leveraging more fantasy based environments - such as Gears, or Unreal Tournament style settings which full confirm the virtual game (particularly Unreal Tournament) aspects of the setting and associated violence as seperated from reality.