well, then she probably would have had a coronary at me wearing Ruthie (age 2) on my back (especially when she was asleep) in a wrap sling (sometimes two shoulder, sometimes as a one-shoulder rebozo style carry)... and worse if she'd seen me first (this was when I did one shoulder because it was easier to do this way) lift her out of my rear hatch from her convertible carseat, drape the fabric of the wrap over one of her shoulders and between her legs, then toss her over my back (not literally of course) and have Damian put his hands on her back to ensure she didn't move as I tied it snug and then let him stand back so I could spread the fabric out more around her. We did an entire long cart full of stuff walmart trip one day during her nap that way... she woke up when we were checking out and I just shifted her around to my hip... because she was a bit cranky and wanted her cup and I don't like a sippy banging me in the back.
Oh, and Ruthie loved the wrap so much that she would grab it and want to be in it up till she was 6 when she wasn't feeling well. I wore her out and about until she was 5, when she just got too big to be comfortably worn for me. But hey, she was sitting in my lap when she was unwell anyway... so if the snug "blanket like" feeling of being all strapped to me made her feel better, why not? Heck, there were times when she was little that she would be in the stroller and I'd have Jeffrey (3-5yrs during that time) strapped to my back. Another way he expressed his jealousy, really, wanting to do another thing she was doing... and why not? he was still young and small enough for me to do it comfortably...
With the harness/leash... I had someone compare my child to a dog (and I made a comment about yes, because I want to keep my kid safe, too, not just my dog, and that they should worry about no one using seatbelts in their back seat), and yet I had someone else (older GENTLEMAN) tell me how good I was to use one when we were at a busy buffet restaurant because that way she wouldn't dash off and I could get my kids' food and she could walk around as she wanted to. (he apparently had my similar disdain for unsafe kids running helter skelter through the place and yet also keeping a child who wanted to be down walking from doing so within reason.
Now I've definitely seen my share of folks who shouldn't be allowed to use them, but the harness/leash in and of itself is not the problem there.