As a cat lover this only strengthens my opinion that they should stay inside the house, humans cause enough damage to the ecosystem without needlessly unleashing pretty efficient predators for no gain.
Not to mention that the cats who aren't too lazy to chase things are far more likely to go for ground-based animals like rats and mice than birds. As in, the rats that would be raiding bird nests if the cats didn't keep their numbers down.
Cats also routinely go into other peoples houses and either get themselves stuck or hunt rats/mice there, also something that humans generally are not allowed to do.
Isn't putting them on a leash, or having them wear a bell around their neck outside, enough for all parties?
I would also say they would at least need to be neutered in that case so they dont reproduce with the feral population, but from a predatory perspective that would probably be fine then.
I would still not let our cats go out, my wife is pregnant so toxoplasmosis is very scary and bell or not we would be terrified of them getting lost or getting run over by a car or worse.