[Itrtuawh]

I have a different perspective than you do. The cats we introduced here are not native (and neither are the rats that came with the europeans) and while it may be "natural" for cats to hunt birds and vermin, this is not their natural environment, so the local native birds are not their natural prey. Native songbirds have declined markedly in recent years in the US (and Canada), and feral cats are a big part of the problem. Feral cats that succumb to the "harsh environment" are also an indication that the environment is not really a natural one for them. I don't think it is doing them any "kindness" to let them live out a short life, eeking out an existence as marginal feral animals decimating a natural population of songbirds and small rodents and reproducing uncontrolled to keep the cycle going. Neuter and release programs can at least reduce the feral population a little, and keep from introducing more kittens into the cycle. So far as the rodents that get into our houses, our indoor pet cats can keep them in check.
I am not meaning this as a personal attack about your feelings on the matter, just trying to give a different view point.