I didn't read all replies...
I think this topic is very regional I think. I think people who grew up/live in the city will have very varying opinions from people who grew up in/live in the country.
And this is something I've been actually thinking on and off about as I have a DS. My father, grandfather, future FIL, and several of our close family friends are all hunters. I live in an area that is BIG into hunting... like, I think some schools around here still close for the first day of buck and doe season and it's not uncommon for majority of the boys to be absent for that week of class for first week of hunting season. No, I'm not kidding... I live in redneck-ville. ;-)
So, I grew up around guns. We had hunting rifles locked up in the house. My Dad and future FIL have already mentioned about taking DS hunting when he is old enough. I have a ton of mixed feelings on this and get this panicked feeling in my throat. I know that before I'm okay with that, I will have to first make myself go through gun safety classes and be present for all of DS's gun saftey training. I just don't think I will feel comfortable before then.
With that said... I like water guns. They are fun. My sisters and I always had a collection of water guns and would have water fights in the backyard. I never ever once equated a toy water gun with a real gun. I knew there was a MAJOR difference.
I was also around toy guns (rifles) due to living in a huge hunting area. All my boy cousins had them, and I had male friends as well that had them, and my youngest sister even had one as she asked for one the one Christmas. These don't look real at all in my opinion and I think I will be okay with those. And the western style toy ones that also do not look like the real thing at all.
So I guess, writing this all out I found my line... toy guns will be okay as long as they are the chintzy non-real looking things. It's going to take me a long time to get comfortable with the real thing... but I know with the area I live in, it's something I'm going to have to grapple with sooner or later, especially come 4th grade or so and DS's friends all go hunting with their Dads/granddads. It's just a total culture here. Parents beam with pride when their DS brings home their first deer.
So yeah... I think it's a very regional dependent opinion. No right or wrong. We each have very valid reasons for the way we feel.