Most cats are not fully domesticated. They are not dogs and it's not in their nature.
/Snip
In my opinion asking people to keep "their" cats indoors all the time is like asking them to enslave an animal
I respectfully disagree with you, and your inferences of cruelty. We cannot make distinctions with pet types as to whether they are enslaved or not. Once we become the primary care giver, with food, managing their hygiene and supplying their need for attention, all of which they would otherwise not receive in the wild, it might be said that we are enslaving them by circumstance.
The dog vs cat comment is a little daft "because they are a different creature". If we are to use the term 'enslaved', the only difference between a suburban yard dog and an indoor cat is the size of the jail cell.
To be transparent here, I live with a cat, Vinnie, in my home. Our home. For me, It's the ninth dwelling I've lived in over my life. For Vinnie, it is the only home he has ever known.
To this, I will add that as an indoor cat, Vinnie gets plenty of sunshine, from sitting on the window sill. He gets plenty of fresh air, because those windows open. He gets plenty of exercise, as I 'play ball' with him every day, or we chase each other around the house. At times I will let him outside to explore, and he is strictly supervised by me, and has never bolted. He is so domesticated that when he encounters a non-human living creature his predatory nature does not snap into action at all, rather he sits there in fascination simply observing.
Does this sound like animal cruelty ? Vinnie was 'adopted' as a kitten by me, from a no-kill shelter, as far as I know is only one of two in my city. As a responsible benefactor to all abandoned or homeless cats, It took four visits to the shelter by me, actually meeting the adult cats, but nothing 'clicked' (This shelter is very adamant about the cats 'finding' their new caregivers, and I've seem them outright refuse adoption to many people for various reasons of incompatibility or other concerns). Another two visits after that, and I came home with Vinnie.
If people did not adopt abandoned cats, what would be the outcome? More feral cats....more destruction of native bird life. No-kill shelters would reach capacity, and no longer be able to claim no-kill status. Without people to counter the reprehensible actions of the people that came before them in the act's life, then feral cat population would become a very big problem, the likes we can't begin to imagine compared to the current situation. So you can sit there and denounce cat 'ownership' (for won't of a better term) as slavery, but I would argue that it's liberation from mass death.
And I want to be clear here. Despite my liberation of Vinnie and the greater environmental benefits of adopting him, I'm no crazy cat guy. In fact, I tacitly support the argument for feral cat culling. It is the greater good that is to be focused on.
Kill one cat to save 10 birds, 30 marsupial mice and 50 crickets sounds like an ethical tradeoff to me. I heard an analogy the other day (Sam Harris podcast I believe) of the ethical 'best choice' dilemma which asks the listener to consider this: if you were to witness a burning house, and inside that house was a child and a Picasso worth $5million, which would you save? Bearing in mind that you would be expected to sell the Picasso, and donate the money towards the saving of many many children's lives through healthcare initiatives? Of course our instinct is to act upon the most immediate and direct humane impulse, and that is to save the child from the burning house. But in doing so, you are invariably killing thousands of other children. The same goes for cat culling. Many would say it's cruel and inhumane to do so, because the greater good is not immediate to our consciousness.