Ok, I haven't read all the responses, but ... Dogs leashes are not to pull them. A dog leash is to teach the dog who has the lead. I have not heard of ONE parent who uses a restrain, or leash, to pull their child or to be able to let the child free and not have to watch them. They use it to keep them safe and avoid the child from wondering off.
When a child is on the leash he/she will walk with you, and is free to wonder within a certain distance. Many times, or the majority of times it, contrary to dogs, it is the parent who is following the child and the child who is leading the adult. When they are approaching a place where they shouldn't be the parent is able to grab and prevent junior, or the princess, from falling, hitting or doing anything that may harm them. Many children outrun the adults and end up getting hurt.
Many others have bought the device because the junior, or the miss, just wonders off. We had that problem with our daughter who was an extremely friendly child who once got picked up by a cashier at Kmart. The woman was standing next to me but when I finished paying and I didn't see her in the stroller I almost died of a heart attack. When she was older, like many here said, she would see something that would catch her eye and would walk towards it completely forgetting to tell me. We bought a hand leash and it gave me the biggest piece of mind because I knew she couldn't go far. She would wonder off and when she couldn't go any further she would come back and tell me where she wanted to go. No need for me to pull her.
Parenting is all about doing what you think it's best for your child. If a parent thinks the best thing is a leash, tether restrain or whatever is called where you live, then it is their right and their duty to use the technique they see fit. Unless they are causing physical or psychological harm there is no reason for anyone to pass judgment over what they do as a parent. Plenty of people I know were raised with a leash and they are productive members of society; I have yet to see otherwise.
As a society we need to be more tolerant and respectful of others people's choices, even if we do not agree with them. It is one lesson that we fail many times to teach our children and that it is, in my opinion, as important or even more than if we use a tether or not.
ETA: BTW since I see some people insisting in comparing dogs to children allow me to say this. When I took a car to drive for the first time (at 16) my mother told me this: "If you accidentally hit a dog, you can accidentally hit a child also. Dogs, the elders, and Children are innocent care free creatures that deserve caring and vigilance. Always watch for them." Yes she put dogs in the same category as humans. But her point still stood high on my mind. We are all God's creatures and it doesn't matter if you are human or animal the same vigilance, care and patience is deserve for all. So from this parent personal opinion I can say go ahead and compare it because if I can loose a dog, I can loose a child too and neither would be acceptable to me. Although I don't have pets.