I'm a mom of a boy (age 3 almost 4) and trying to decide where I stand on this. I don't have any brothers either so I didn't grow up with boys around. So this boy thing is new to me. At first I was a no guns or any weapons for toys but then I started to change my mind.
*I'm interested in hearing different opinions because I'm not really sure how I feel about all this and where to draw lines on what toys are allowed, what type of play is allowed, what type of cartoons to let him watch, etc
We don't allow any toys that look like real guns but there are so many other weapons and fighter toys - like many boys he loves transformers, super heros, pirates, knights. All of these things fight and many use some kind of weapon. He's never seen the transformer movie, starwars, etc but has seen the cartoon versions and just learns about all this from kids at school and other places. He now has toys that have weapons on them (transformers, pirate legos, Buzz lightyear toys, etc though I usually remove the weapon if it can be removed). But even withouth weapon toys they will turn things into weapons - he decided that the Thomas the train railroad crossing gate was a 'shooter' and was using that to shoot something. He will build swords and guns out of tinker toys and legos.
I think the most important thing is to teach your kids about right and wrong, violence, guns, etc. But its the playing and tv watching where I'm not sure where I stand on how much to allow. At first I was no weapons allowed, then I bought him a sword as part of a knight costume last year and since then have allowed a lot more of these toys. He loves to talk about 'guns' and 'shooters' and they don't like the kids to talk about this/play this at school. I feel more ok with a sword but I think this is because people don't fight with swords today.