I have to say my DS and all his friends have played COD since primary (he is 14 now), but they've also played lots of non war games like Fifa, Minecraft and so on (they spent quite a while last year all playing Minecraft in a group on xbox live). The only ones that didn't play were the handful who had PS4s (so were playing but on a different format) and maybe 1 or 2 who weren't allowed. Those boys have ended up pretty isolated, because there's so much chat goes on in the games that it's hard to fill someone in at school the next day every time.
My DS2 is a lovely boy, very sensitive and not at all violent. Most of his friends are lovely, polite boys as well, in grammar schools (DS isn't so not a stealth boast!) and all have played for years, but a variety of games not just one violent one.
I think not being able to afford the game is one thing. If the reality was there wasn't money to pay for it, or the console, or the x box live sub, then he'd have to do without, or maybe a paper round etc to contribute.
But if it's because you don't like the idea of the game, what do you think it's going to do to your DS? His friends play, what are they like? Pretty normal almost teenage boys I expect. It won't turn your DS into a monster.
As for finding new friends...i think in an average school boys who don't game are in a pretty small minority. And nothing to say those boys btw are going to be nicer, or better, or ones your DS should be friends with. They'll just be ones who don't game. Not necessarily the same thing.