When I visited my friends who had indoor cats, they always seemed either timid or bored, spending hours just sitting looking out windows or sleeping.
I always found it hard to watch a cat staring out at the world, with their only stimulation/interaction happening in the small amount of time each day when people were at home and not busy with something else or sleeping.
I’d argue the same about humans, frankly. The only ones content to stay indoors all day are those conditioned to, and damaged by, the captivity.
The only cat that lived a short life had nothing to do with being allowed outside. He was the most unique cat I've ever encountered. He'd could use door handles, play fetch, come and get you if he wanted to go out and the cat flap had been locked for whatever reason, would wait for me at the end of my road when I walked home from work and would then wait for my to start running and race me to the front door. Sadly he was born with a condition that meant he passed away before he turned 5, but he was happy and playful every day. Losing him impacted me more than I would have believed possible.
Anyway, I just wanted to say that it's not such a binary choice. As long as you don't live right next to a road with lots of traffic, cats that can come and go as they please don't necessarily live short lives.
It's just idiots who think all cats can learn to live alongside fast cars that end up with young dead cats.
As it so happens, a lot of places in this country, even in many cities, may be near green spaces and preserves where these kinds of wildlife can be found.
Sure, traffic and horrible people who think it’s fun to torture animals to death are an additional concern in more densely populated areas, but they can also be a threat in less densely populated areas.
Unless you have a barn where mice thrive, it is not advisable to let them out to eradicate the local songbird or amphibian populations.