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If there was proper storage, why would the parents be upset? ...
Emotions rule over logic. It doesn't matter why, they just are.

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If there was proper storage, why would the parents be upset? ...
My parents were a bit of a contradiction. They raised us to believe in personal freedom and the rule of law, but we weren't even allowed to play with toy guns, let alone shoot real guns. (Squirt guns were as close as we got, except when we were at friends' homes. Did we play with their toy guns? Oh yes. Did we enjoy it? Oh yes. Yes we did.)
I got into the gun game much later in life than most of you, but I have become the evangelist for the family and coworkers. I have taken three of my coworkers shooting. One of them -- a Bulgarian -- always supported the right bear arms and loves to shoot. A second -- an American -- said one of his pre-teen daughter was upset when she saw him ogling guns in a sporting goods shop, but he is likely going to join the gun owner ranks in the next few months. A third -- an Indian (dot, not feather) -- had never really considered gun ownership or use. When I asked him if he would like to shoot, I could see the wheels turning in his head, but he readily agreed. He had a great time (so did I!) and I think he'd like to go again.
This past weekend, we had our annual birthday party for our three sons. All four of my siblings were there with their children. I ended up showing them my Liberty safe, my M&P9, and my Remington 870 Express. They *asked* to see them because they never have. My sister-in-law's eyes got wide when I produced a loaded M&P9 from my bedside lockbox, and then walked her through the process to unload it and verify that it was unloaded so we could safely handle it. I need to take her shooting. I think thereafter she and my brother will become gun owners, and that's good, in my opinion. The old evangelical mantra of "each one reach one" is the best way to ensure this cornerstone right is preserved. When you convert parents, you do more than reach one because you also reach their children.
Those of you who were raised around guns by responsible adults may lack a certain perspective: those of us who handled, shot, and owned our first guns well into our adult lives were nervous the first time we were even around a loaded gun. Why? A loaded gun is a deadly weapon and is inherently dangerous. It's a big deal, but by holding somebody's hand as they see, handle, and shoot a gun for the first time you attach responsible humanity to the object. You demonstrate that the inherent danger of a gun only becomes manifest danger when a person is involved, and also that said inherent danger is managed properly by responsible people.
Besides, shooting is fun!
I think this thread has made some great points. I also think the OP did a fine job of difusing the situation.
Yet now I am conflicted.
If there was proper storage, why would the parents be upset? Even Sarah Brady could not fault me on my gun storage or gun safety. When my kids were young, they went to people's houses. I knew the people but did not always know if they owned guns or not but would assume they did. Having a gun safe, vault or whatever should have told the parent that the home was a safe area.
Now if the people were anti gun, they might need to move to another state. Do they ask other parents if there are guns in their homes?
Also there are a lot more things in homes to be concerned about than guns. A medicine cabinet holds a lot of deadly items. Many kids have been killed or injured by yard tools.
Good on ya...how can anyone know they won't like something until they try it...this is how I got a lot of celibate girls to become loose.