I find it horrifying! not sure why parents would want their children pretending to shoot other humans dead
Really it's not a whole lot different to the kids re-enacting fairy tales - Sleeping Beauty gets a curse put on her and she is supposed to DIE originally, but the good fairy changes it so she only sleeps, Snow White was going to be MURDERED by the hunter and Hansel and Gretel were going to be EATEN by the witch - so I would assume that you would also find it horrifying for children to re-enact those as well?

It is 100% your right as a parent to stop your children from playing those types of games, but just be aware that you could be creating a double standard kwim? I think it is far more effective as a parent to talk to your kids about the games they play so that they understand what they are doing. Many little children wouldn't have a clue that playing 'guns' can have other connotations and that even pretending to shoot someone dead isn't really a nice game to play. Otherwise to ban it outright is pointless because they 1 wont understand unless you explain to them why you don't like it and 2 that we can only protect them for so long - sooner or later they are going to be exposed to external influences from other children, children who may or may not be allowed to play those games as well. So the child that you have prevented from playing violent games will one day come home raving about playing like that with other kids and want to replicate that in the home.