Hmm, funny you mention birds. Do non-American cats not destroy bird populations? Do they not get hit by cars? Do they not get stolen? Do they not catch diseases such as FPV? Must be weird American things, for sure.
If you cannot read your cat's emotions, I feel very bad for your cat.
Every expert and humane society will agree: keeping your cat in is the humane and smart thing to do. You can't even argue otherwise because it's just proven to be the case.
You're letting your headstrong opinions harm your cat and your ecosystem, a truly American approach. So, congrats, you'll fit right in with everyone else in America that lets their cats out (something that you seem to think doesn't happen in the US, for some reason).