Letting your pets wander around is no more "humane" than letting a toddler run around.
I think this is slightly hyperbolic. A 1 year old cat is much better equipped for survival than a 1 year old human. Otherwise you probably wouldn't be seeing many cats outdoors to begin with. If you don't believe me, consider this experiment: Get an angry pissed off dog and unleash him on a 1-year old cat. The cat may get hurt, but his odds of survival (by fleeing) are actually pretty good. Now get an angry dog and unleash him on a 1-year old baby. The baby's chances of surviving aren't going to be anywhere near the cat's. I don't think comparing a pet to a toddler is fair, they're built too differently.
I would like to say that there are some practicality issues with cats+leashes. Unlike dogs, who let you lead them, every cat I've attempted to "walk around" would always just do his own thing. You can't take a cat on a walk without literally dragging them. Also, wandering cats are common, and territorial. If your cat is leashed in your backyard, and a particularly nasty neighbor's-cat wanders into the yard, your cat being leashed may actually put his health at risk.
Some cats aren't happy as indoor kitties.
Some cats aren't safe outdoors.
Keeping your pet safe and happy is a balancing act.
Anyway, while a pet-tracking GPS unit isn't going to save anybody's pet after it gets into trouble, it could still be useful. For instance, if you know based on previous-GPS tracks where you cat tends to hang out and travel through, the information would allow you to more efficiently search for where they are if they go missing for a day.
Besides, I think there are fun reasons to slap a GPS on a cat that have nothing to do with trying to ensure their safety. I'd probably do it if I had an outdoor-kitty. (my current cat has to stay indoors for medical reasons).