I agree that we need to think about how to nurture bird populations but keeping cats pent up indoors is wrong - and is reflected by how much worse they behave when that is done.
Sketchy link to a PDF by UC Davis. I was looking for a reference on the average lifespan of an outdoor cat, which I always here quoted around 2.5 years. It's a little write-up on why it's maybe not so nice to let your cat outside.
Maybe it's different in the UK, but I've seen a number of drivers speed up and swerve in neighborhood streets to run cats over. It's fucked up, but it's a thing. I remember having classmates in high school that would brag about it.
Add every other danger, jumping into a backyard with the wrong dog, parasites, coyotes, and it's not exactly an idyllic stroll even for indoor/outdoor cats.
I'm sure dogs aren't allowed to wander the neighborhood in the UK. I would have no problem if they confined their cat to the yard or let her out while supervising.
Our two cats are quite fulfilled and pleased with their situation despite only going outside on leash.
Does anyone have better researched numbers?
All bar one of the cats that I and my family have had were outdoor cats who lived much longer than that. The exception was run over crossing a dual carriageway to her favourite hunting ground. The latest one of mine lived to nearly seventeen and went out in the woods pretty much everyday. He slept at home in the house though.
Prioritizing the feelings of "my cat" over "all the creatures that will be killed, all the neighbors who will have to clean up after my cat, and all the gardens and bird feeders that will suffer damage" is a mindset that is so selfish and myopic.
If you cannot give your cat a quality of life indoors that would not be cruel, you should not own a cat.
What? It's absurd on its face. The only reason cats get this treatment is because we've traditionally allowed it.