We tried the indoor cat thing. Lost our old cat in a road accident, he was nearly 7 and we thought he knew what he was doing around roads. But something went wrong and it was heartbreaking. The two new rescue cats arrived a few weeks later and we swore they would be indoor cats. That lasted four months (November to March) and then we realised that we would actually need to open doors and windows on account of spring arriving. Couldn't afford epic cat-proofing of the garden, and the layout at the rear of our house would have been really difficult to cat-proof anyway. So tentative freedom was granted to them. Both neutered, obviously. Older one rarely goes out and is always nearby. Younger one roams more but is never gone for more than a couple of hours without popping back to say hi. Both get shut indoors overnight, and they're not allowed to go in or out of the front door (to discourage them from hanging around near the road). Younger cat does wind up the neighbours' dogs a bit, purely for existing rather than because he's doing anything to goad them, but that happens even if he's just sat on the windowsill (inside).
We're lucky in that they are both so attached to the litter boxes that they don't toilet outside, at least to the best of my knowledge. There are certainly enough poops to scoop every day to suggest that they do all of their business indoors. Youngest cat even goes out for a while, returns to use the litter tray and then goes back out again! I think this habit might be linked to their life in 'captivity' while with Cats Protection and their lives as indoor-only cats for 20-ish weeks when they first came to us.
While I could see the older cat being pretty happy staying indoors at all times, it would be difficult to manage as she'd be bound to get curious when it's summer and the back doors are open for ventilation.
But I'd be really sad if I had to keep the younger cat indoors all the time. As much as I fear for his safety when he's out and about, I can see just how much benefit he gets from it and would hate to deprive him of that.
Yes, you don't let any other animal out to roam unsupervised. But that's either because they wouldn't come back (rodents, bunnies) or because it's physically impossible (fish) or because you can easily take them out 'supervised' (dogs). Cats are a unique category of pet. Comparing them to dogs in this respect isn't super helpful, as while there is always the occasional story on the internet of a cat in a harness and lead enjoying its daily walk, most cat owners know that trying it would cause massive distress to the cat and (probably) a bunch of nasty scratches to the owner.