YAMBU OP but you are fighting a losing battle (no pun intended).
So much of our popular culture, including that aimed at DC, is based on war, conflict, fighting, good vs evil etc. It doesn't matter if your DS never sees it himself, the stories are in the playground and woven into playground games.
DS and all his friends at nursery played gun games (with their fingers) despite none of them being exposed to that kind of thing on telly, but some of them have older brothers and sisters, they teach the games and on it goes. It's part of the culture we live in.
FWIW the DC's nursery, which is the most hippy / right on place you could properly imagine, has a policy on war games. It's simply that they allow the DC to express themselves when at play, and they only stop play if the DC are at risk of harming themselves or each other. No ban on war games.
I used to try to ban DS from war games but I've changed my views as he got older. He wanted to so much, it became an issue and was making the whole thing into a bigger issue than I was comfortable with it being.
Plus a (very lefty!) adult friend of mine got two nerf guns, one for her and her DS and talked about how much fun it was for her. And that simple thing reminded me - yes, actually, playing with water pistols / at Lazer Quest when I was young was great fun. I probably would have would have enjoyed Nerf guns.
So now the DC are allowed guns. But DS (who at 8 is old enough) understands my thoughts on war. Instead of banning weapons, I rry to counteract the war-is-good message in other ways. We talk about war and what is going on in the world at appropriate times. DS knows I don't like weapons or war.
I sometimes sing him peace songs at bedtime (he loves "last night I had the strangest dream") and I encourage him to think critically about war. We talk about how good and evil is a great plot device in stories but how things are usually more complicated in RL.
He knows my feeling on war and explains to me with the patience DC use when grown ups who are being a bit stupid "but it's just a game, mummy, it's not real war" and these days I'm inclined to agree.