Interesting discussion. When I was young we all had guns - girls and boys - and we played cowboys and indians or battles. Not much was thought about it in those days and we didn't grow up to be a bunch of gun toting killers.
If I had a little boy, I wouldn't be concerned if he had a cowboy outfit and the holster and guns. Having said that, I wouldn't let him outside of our enclosed garden with them just for fear of extreme reactions to the guns as was pointed out earlier, ie. police thinking they were real, etc.
I think the water pistol or ping-pong ball gun sounds like a good idea if you want a compromise.
I would also suggest a list of presents from Santa and say not everything you want you get
It's a shame the world is such a harsh place where imagination can't be let run riot for fear of reprisal.
I hope you find a nice compromise for him hun
