Anyone that equates a child to a dumb animal is sick. And we do have laws that will take your child away for neglect and such abuse.
So, if your child is playing in your yard, someone comes and scoops him up, and then drives away - you should be convicted of neglect? It’s the same logic you used. You should have kept your child in the house, right?
The cat was on the owner’s property. That should have been enough. Whether inside the house, on a balcony, or watching people in the yard, it doesn’t really matter, does it? Same goes for cars, trucks, people, whatever. If it’s on your property, other people shouldn’t take it.