Ah yes, another attempt at 'I need to appear in the media; let's make a controversial statement'.
This explains why town planners are spending all their time in SimCity.
Would someone please sit this person down in front of a shooter, and then ask them to fire a real gun based on their preceding experience? Nothing like the same thing. Not one bit. No, funnily enough it's training people to shoot guns that enables them to be able to shoot guns.
So at best, this is about psychology of shooting stuff, and the vast majority of targets in modern shooters are zombies, more zombies, terrorists, pirates, Nazis, Communists, soldiers from <insert country other than the player's here>, even more zombies, or, occasionally, animals.
Presumably Saints Row the Third should already have caused large numbers of people to be beaten to death with a over-sized sextoy. The preceding fallacy makes as much sense as the original statement.
Also, I realise it may be a product of sheltered upbringing and/or pure luck, but clearly such people have never seen real blood or real injuries. I can assure them that the experience of helping someone who has been seriously injured, getting their blood all over you, smelling it, and having to clean it off (all of which ironically probably meshes fairly well with proximity of having *caused* said injuries), is not even remotely equated in videogames. Desensitising? Only if damage causes mild red bars at the edge of my eyes and guns go 'pop' instead of a really loud 'BANG'.