I'm a closeted gay parent, and I agree, there's developed a kind of assumed quarantine zone around any child that is not your own. It's completely different than when I was growing up. If we were at a friend's house playing and got into trouble, it was assumed by all our parents that whereever the problem arose, that parent dealt with it, then called the other parent(s) and you got it again when you got home. No, I don't mean corporal punishment (those were rare and only at home and only after multiple warnings; not saying it was the right way to handle it, but it was definitely not a moment-of-anger response either).
But today, the quarantine zone is essentially universal. If someone is visiting someone else's house, it's assumed each parent is to keep order with their own child(ren). There are only a few people where it's assumed OK for them to approach our kids for hugs, or to have them sit with them on the sofa to talk, or whatever. Back in the day, it was assumed when you went to your friend's house their mom would greet you with a hug, maybe a kiss on the cheek, and a reminder to be good.
Seems like a hyper-paranoia has taken hold among parents, at least at younger ages. Given the sexting and sex-with-teacher scandals in schools lately, there seems to be a disconnect in the way parents approach hyper-protection in grade school and it's like they turn off a switch when the kids transition to middle- and high-school. Very odd, I would think middle school at least would garner more scrutiny by parents given the inherent opportunities for issues as the kids mature.