Poison kills many different species not just the target species, including cats, dogs or owls who find a dieing or dead critter an easy meal. Yes if you have a bunch of dead mice laying around they are snacks for a dog, cat, skunk or whatever. I raised mice and sold them as a kid so know what those critters can take and now many species feed on them. I supplied about 50 mice a month to a couple pet stores, usually for snake food from about 8 years old till maybe 13. We raised pigeons, hunted, fished year around as well as hand dug large gardens all for food. I grew up POOR while rescuing a kitten was something we could & did do taking it to the vet was not in the budget as taking us KIDS to doc was not in budget (real easy to figure out when there is 0 money!) We kept a cat or two around with only rare small bag of food 2 or 3 lbs lasted a month, the cats ate mainly from mice/birds they caught. Some of the happiest animals we ever had were ones that would go hunting in fields or woods with us. They got the spoils of a good hunting trip or fishing trip (innards of the soon to be dinner for mom and my brother.)
People having this holier than though attitude is not something I cotton to. Lots of people say they were poor yet they had/have phones, TVs, Cars, electric & heat and parents with jobs earning money for those luxuries. I grew up with 3rd hand clothing hand-me downs from my brothers who got it from others.
Again just because you say un vaccinated cats spread disease it is less likely than Vets and Vaccine companies want you to believe. If the cats are healthy, fit and are able to feed themselves without eating poisoned dead mice they live long, healthy and happy lives.
Mark