While I feel strongly against allowing cats to freely roam neighborhoods, encouraging cats to walk on a leash and harness or creating protective outdoor environments can be terrific. Cats can also 'go for walks' in super luxury kitty strollers. For many (not all) cats - such experiences are wonderfully enriching, and safe!
Other animals (which may threaten cats) can't get in, and the cats can't get out.
While being indoors IS SAFER - the problem is that our homes are sometimes simply boring places for cats. With little to do, except to eat, so many cats have grown around their middles - and being overweight or obese often leads to a long list of diseases, including arthritis and diabetes. What's more, Dr. Tony Buffington of Ohio State University College of Veterinary Medicine has proven that stress related to living in a non-stimulating environment can cause idiopathic cystitis, which prompts cats to miss the litter box. When that happens, the human/animal bond can break, and cats are relinquished to shelters. The stress and boredom of living in an unenriched environment can contribute to an additional long, long list of problems, from cats having accidents to various other physical issues.
Knowing this - several years ago Buffington began a website on this topic, including tips on enriching environments for indoor cats, called the Indoor Cat Initiative,
and I (and others) began to speak to veterinarians and cat owners about enriching environments for cats (as well as dogs). Clearly, cats living in enriched environments appear to be happier, and certainly living in interesting or enriched homes is beneficial to their health.
While some cats may be terrified of being outdoors - even being pushed in a stroller, or playing in safe outdoor catios - most cats seem to enjoy taking in the smells and sights, and figure it out, that they are protected.