There probably is a relationship between playing violent video games and those likely to knife people and be violent, however people rarely seem to consider the direction of the relationship. Isn't it that violent people prefer to play violent games, rather than violent games make people suddenly that much more violent? Nobody can deny they do have an effect, but one that is on par with a competitive game of paintball, for example.

Why not just make exposure on the Armoury optional? A simple tick box in the character options.