Raised properly… to not go exploring every nook and cranny? Personally, I’d rather let them be curious, and take steps to be sure they can explore safely.

Rather than thinking of it as a person on a leash, compare them to strollers. You see kids in strollers all the time; they’re strapped in, don’t really have any control over what’s happening, and kinda have to be passive. And they’re generally pretty happy like that for a while. But, not every kid is alike, and not every parent has the resources and help they should have. A leash lets a kid run around without the stroller, without getting into trouble where their parent can’t immediately see what they’re doing. It’s a step between being strapped into something, and running around freely.