OP, just do what you need to and don't worry about what someone else might think. You'll never see those people again anyway. I found something kind of interesting when ds was that age. He was a "runner" too but when he had the harness on, he would actually calmly hold my hand for the most part. I guess when he had it on, he knew there was no point in trying to run off. So for us, it aided us in training ds to hold our hand and stay with us. He also loved climbing the stairs on Tarzans Tree House (and later at DL, the Swiss Family Robinson tree house) and it was a nice added safety measure to hold his hand and have the harness on. The harness got us through a phase.
Totally OT, because the OP was talking about their 2yr old, but I also wouldn't judge someone with an 8yr old in a harness because I don't think the average 8 yr old would allow a parent to put one on them. I would probably think that person has an unseen disability (like autism) and the parents are doing what they deem necessary to keep their kid safe. I agree, I would be judgemental if I saw them using the item to mistreat said kid though. I've never seen that happen.
Not that I'm doubting the other posters, because maybe I'm just in my own world when I'm on vacation, but I've only seen one instance of "leash misuse" when at WDW in all our trips there. That was with one of those stretchy leashes that look like a phone cord that stretch about 20' and attach to the childs wrist. Poor child was lagging about 15' behind the attached parent, and the parent didn't seem to be aware. They all looked pretty tired, actually, lol. My thought at the time was that it was a tripping accident waiting to happen. I think the nature of those types of leashes makes it too easy for the parent to lose their attention on their child and "forget" them. Totally different than the one the OP is considering.