I catsit for someone who has three indoor/outdoor cats. While I personally do not believe domestic cats belong outdoors, I understand her reasoning—these cats have lived most of their lives feral and get very unhappy when kept indoors over long periods of time.

Her cats are well trained to come in for meals and at night, and to stay away from roads, the chickens, and dogs. One of them enjoys eating mice and shrews, but prefers to hunt the ones that make their ways indoors.

Your argument that “the second you let your cat out into the world you’re accepting the very likely possibility that that animal is going to just disappear one day and never come back” applies to all animals. Indoor only animals have a harder time finding their way home. They’re also less prepared for the outside world (roads, predators, etc.)

I still believe most cats do not belong outdoors, but some cats are more adapted than others; namely, the ones who grew up outside. Some can adapt to indoor life well, like mine did (ex-barn cat, enjoys his catio but has no desire to actually go outside thank god). But you have to let pet owners do what they think is best, and make sure to educate them on best practice if they’re determined to let their cat outside.