1. I'll use myself as an example. You meet me at a store. I'm no small guy. 6'4. Just above the 200 line for weight. We all decide to meet at someone's house. Now... what you know of me so far? What you see and what I choose to tell you. Could be a complete lie...could be the complete truth. Strangers in my house? I pass. (Never mind the fact that I walk around with an FN Five-Seven. ...that always gets people skittish and wondering if I'm a robber... *groan*)
2. In fictional land, I'll be a parent. My son who is 14 loves being creative. Meets a group of older boys / adults at the hobby store. I haven't met these people.. but I know I've watched To Catch a Predator and CNN lately. I don't mind if they play at the store, but no snow ball chance in hell is my son going to an adult's house who I don't know well. (Triple that if I have a daughter.. ...happily, the wife hasn't sprung the "...I'm pregnant!" trap on me yet.. ..but time will always prove me wrong.)
Maybe it's a US vs UK thing or maybe I'm just somewhat over-trusting - but I really have no issues with either of those and they seem frankly paranoid - walking around with a gun, much less an obvious one is something that I can't even correlate to as it's not done here - but I'm easy to let people into my home or go to other people's home, and provided I'd at least visited first I'd let my children go to a game at someone else's house (well not at 16 months, but it's hardly an issue as she can't talk yet anyway).
I mean no offense by this (I know next to nothing of your circumstances), and I'm hesitant to post in case it's taken the wrong way - but in my experience there's very few nasty people in the world - they just get all the publicity.