Many modern multiplayer online games are about player cooperation. As a player, you usually join or form a guild / tribe /clan with other players and work towards goals as a team.
I believe this can be beneficial as there are people of all ages from all over the world in these teams. They use online chat to converse and plan strategies to help or defeat other player groups.
Some players have been playing the same game for 5- 15 years. Player groups have real life social events and even real marriages have occurred from meeting online in a game.
From my experience, the most common danger is forming an addiction to games, when you go through periods of falling asleep and waking up thinking about a game. This has a broader effect on relationships and socialising.
My opinion is that for someone to be inspired by a game to carry out some atrocity, there must be other factors like mental illness or drugs involved.
I doubt there has ever been a more despicable time in human history than the second world war. Human beings did every sick thing possible to other human beings. What was their influence?