First, I'm really sorry you had to witness that, I cannot imagine. How devastating.
Judge me now, I let Jackson out in the backyard at my dads house. He's not 100% supervised at ALL times but with that said, he's never out more than 3 minutes anyway and then he's back at the door waiting to come in. At night, I stand on the deck and watch him go potty and he comes right back in. We're secluded though, very country. All farmland behind us.
If we were in a neighborhood that my aunt lives in, for example, I probably wouldn't. Every house's fenced yards are somehow connected (like each house has their own fence, but they're right up against each other) -- busy roads close-by, dogs on each side, lots of traffic, lots of people walking around. Typical suburban neighborhood.
It's hard to explain my dads house, but it's very rural, very safe. My dad is very anal about the fence and keeping the yard up. He only got a fence specifically for the dogs. We also have a camera (he owns an alarm company) out back and can see it on a little TV screen up in our kitchen in the corner (we have a pool, so always want to be able to see).
I will say though, I saw a coyote walking through a upper class nice neighborhood (not by my dads house, different area). I thought I was seeing things but then saw reports of one being there! I had Jackson so I was spooked and immediately turned back around. Don't know if it even saw us, it went into the woods. But they're definitely around, even if not common. And this was a super nice expensive neighborhood, not 'country' at all.
But *shrugs* I know I'm not a bad dog owner, in fact I'm pretty much a great one if I may be so modest, and I'm not going to hover over top of my dog every minute he wants to be outside and ... be a dog. To each their own. But I don't think it's fair to criticize and think one is being irresponsible simply because they let their dog out in a fenced in yard.
Obviously, leaving ANY dog outside in a yard ALL day long with hardly any interaction is extremely sad. I'm not advocating that. I also saw a story the other day on the local news about a missing Yorkie they believe was stolen. Owner was crying and saying how the dog would go outside every day, and cross the street to the local kids park and say hello, and always come home, etc. Ummm, duh! The fact that a dog that was left loose, not in a fence, every day and you expected nothing bad to ever happen is just ignorant. That's a different story IMO. Most people that have fenced in yards and dogs are going to utilize them. I know many people that get fences specifically
because they have dogs. To me, that's being a good dog owner and being responsible.