Here is my controversial take: if it is true that a cat needs to be let outdoors unsupervised in order to live a happy life full of enrichment, then we should not have pet cats at all.
TW: Discussions of animal death.
Letting a cat wander outside unsupervised is cruel both to local wildlife, but also cruel to the cat.
Letting cats outside is often introducing a non-native species to an ecosystem which has not evolved to deal with cats. How is it any different to us accidentally introducing invasive rats, weasels, and other small predatory mammals into ecosystems? We invest a lot of money into ridding sensitive ecosystems of these invasive species but we turn a blind eye to cats because we selfishly benefit from them being around us, whether it's because we find them cute or because they provide a practical use for us as mousers.
I'm fed up of my neighbours cats who visit my garden. They poop in my planters where I grow vegetables that I eat, which presents a serious health risk to me. The cats predate the birds who visit my garden, which has exclusively been successful on fledglings and other young birds. So far, it has not been a species that is vulnerable and it's only common garden birds, but cats will kill indiscriminately and I have heard many horror stories of endangered birds being predated by cats owned by friends-of-friends.
A pigeon couple has been building a nest in a tree in my garden, but this morning I saw it was predated. I found a chewed open egg, and when showing a photo to my ornithologist friend she theorizes it was most likely a cat as the puncture into the egg shell will have been cleaner if it had been a predatory bird. Predation is a natural part of life, but this predation was not by a natural predator which is part of our local ecosystem and thus I am very upset...
But not only that, I believe letting a cat go outdoors unsupervised is cruel to the cat. Cats so often go missing, more often than not killed by cars. In other countries there are dangerous animals who can kill cats. This is not an issue here but I have personally had to dispose of dead cats who turn up in my garden after being run over on the road in front of my house. I don't think there is any other common pet animal where we so easily expose them to dangers we cannot protect them from.
Just to say, I do not hate cats. I do not blame the cats for pooping in my vegetable beds, or hunting on my property. They are animals only doing what their instincts dictate, and often are doing what we ourselves have taught them when we first domesticated them. Equally, to a degree I struggle to blame some cat owners as people will often argue that keeping a cat inside is cruel, and they do not desire to be cruel to their cats. The intentions are good, and education on this matter is poor.
There is an issue here which needs to be discussed, and the hypocracies we have normalized need to be challenged. For me, I feel that cats either need to be kept indoors if we can verify that this is not cruel to the cat, or we should be required to supervise our cats outdoors like we are supposed to do with dogs, or we should stop having pet cats. Having unsupervised outdoor cats is unacceptable.
Edit: Grammar and adding a TW just to be safe!
