I had been very worried about allowing my children to play such games, and in their early years even banned any kind of toy gun in my house. Eventually i allowed cap guns, nerf, light sabers etc. As they aged, they got into historical swords, and airsoft.
Then we eased into games.
Throughout all of this, I have been an active part in talking to them, explaining to them and imparting my morals on them.
We have no actual guns in my home. I am for gun control and quite liberal.
I have not seen any change in their morals or views since childhood. I think they are well adjusted. They like history and ancient weaponry and fantasy.