(Male perspetive.) DS1 is not at this stage yet, and hopefully won't be for a while yet. However, I can't see that it's possible to win this battle for a majority of boys. (As always, there will be exceptions.)
For me, it's more important that DS1 learns how to react well to testosterone surges than what he plays with or how. Any rough or violent side to that needs to be managed carefully (I don't think that's going to happen within a nursery) but that's a different thing to saying that little boys shouldn't be allowed to have games where they are violent.
If it's not toy guns being fired without contact, I suspect it'll be swords where contact does happen, and if not this then even more inappropriately violent games/mimicry.
He's nearly 3 and since about a year ago, we have played rough games, where I "go to sleep" and he "wakes" me by falling (then) or jumping (now) on me - but with rules. (e.g. away from the head and groin.) Once the testosterone starts kicking in properly, I want to have some rules in place to manage it.
A nice byproduct of this is that I think he had a better idea about limits in treating DS2. I think he's more gentle because he gets to be rough in a controlled setting where he knows that the normal rules don't apply.
I think much of this debate might be informed by worries about ill-controlled aggression rather than guns. The american nutters are correct that guns don't kill people (though it's a damn sight easier to kill with one!) and I think the focus needs to be on who our kids are rather than what they play with.