The first time you kill another person in a videogame, it's a little shocking. You destroyed that bundle of zeros and ones that was made to emulate another human! Inexperienced players especially feel the need to physically cleanse themselves after playing a violent videogame. The article "Macbeth and the Joystick: Evidence for moral cleansing after playing a violent video game" by Mario Gollwitzer and Andre Melzer examines this effect.
The “Macbeth effect” denotes the phenomenon that people wish to cleanse themselves physically when their moral self has been threatened. In this article we argue that such a threat to one's moral self may also result from playing a violent video game, especially when the game involves violence against humans. The cleansing effect should be particularly strong among inexperienced players who do not play video games on a regular basis, because frequent players may apply other strategies to alleviate any moral concerns. Seventy students played one of two violent video games and were then asked to select 4 out of 10 gift products, half of which were hygiene products. Inexperienced players reported more moral distress when the game involved violence against humans (compared to violence against objects), and selected more hygiene products in this condition than frequent video game players. Frequent players, on the other hand, reported less moral distress, irrespective of the game they played.