In the country, I've always free ranged. In town, a chicken tractor moved several times a day. Never had a predator death, as I have a dog like the aforementioned REX! No hawk would dare! I also have a silent, quick predator in my yard in the form of my other dog. No warning bark, just a quick death.
I, too, feel that penning birds up just keeps them in one place for the predator buffet. I don't lock up my coop...ever! Pop door wide open at all times, for a quick getaway should the need ever arise. I agree with another poster about the quick birds being the survivors. A most desirable trait to be passed along.
I feel very much pity for the penned and cooped birds that never run over emerald green grass, scratch through the garden, dust in the thick dust that hasn't been trampled down by other birds.
Walking over a barren run, devoid of cool, green grass, picked clean of forage, bugs, worms, etc., walking constantly over each other's feces, breathing in the ammonia of an overused run and coop. Can't get away when a mean bird picks on them, can't keep other hens away from their chicks, can't select their own greens...must just take what is given. Can't go off alone if not feeling well, thereby exposing other chickens to their illness.
Not a healthy life physically, or mentally, for any animal. Like keeping a dog on a chain or in a small kennel all the time.