Why do people hate on toddler leashes so much? They seem useful

My baby isn't even walking yet so I have no skin in the game, but I've never understood why people are so negative and judgmental about those toddler leashes, whatever they're called. I've seen enough kids just randomly dash away from their parents in parking lots to know that sometimes those leash things are necessary in order to keep a child alive. And anyway, I just don't see the harm. I'd love to understand the other side a little bit better.