Long time ago when my son was growing up, I used a leash with him. This was 35 years ago. He was a runner, not a sitter. I was not ashamed to use this leash. I was only interested in his wellbeing. Some children are just harder to control. It was not a parenting problem. I never noticed anybody making faces or comments. They might have, but I was only concentrating on my son, not the people around me. And I didn't give a rats butt about anyone else's opinion.
I will only say this...
If it's not something which can be controlled by parenting, why is it you hardly ever saw these things 20, 30, 40 years ago (your case notwithstanding)? Yet, you didn't hear of people losing their kids all of the time.
Our society has gotten lazy in so many areas and parenting is one of them. Not saying you--or anyone else here--are lazy parents but I see it all of the time (I know you see it also). It's HARD being a parent and trying to always be consistent. Kids try your patience. They are much more persistant than we are. They also don't understand why we don't want them to do things. I get it, it's not easy.
My point is, I've seen many people who would rather take the easy way out (could be a leash, could be letting the kids watch TV or play games) rather than taking the time to teach their kids to do the right thing. I see parents (at Disney and elsewhere) who barely pay attention to what their kids are doing. They let them do whatever it is they want to do. No punishment when they do something wrong. I constantly keep an eye on my boys to ensure they're not doing things they shouldn't be doing--like walking in front of people without paying attention, running around like a mad person (we have a rule--when in public places like stores, restaurants, Disney World, etc.--there is no running allowed unless there is a place for it). Do they sometimes try and get away with something? Absolutely--and I wouldn't have it any other way (it's how they learn and grow)--but I am always quick to stop them and punish them if needed. And you know what? It's
hard to do this. It takes away from my enjoyment of what we're doing. But it's what I signed up for as a parent. So I do it (as does my wife).
Our younger son boy wanted to bolt. Yet, we've never used a leash in countless Disney trips and other trips. We were stern with him if he tried to bolt. Eventually, he got the message and stopped trying.
Are there exceptions? I'm sure there are. However, for the vast majority of people out there, a leash is not needed and, quite frankly, is (in my eyes) demeaning to the child. I would use a leash on a dog but I'm not using it on my child.