Hello Grago
1 Cancer: Yup, stress, pollution (food/water/environment), genetic disposition ++
2 Cats: A single female can reproduce in a range from 100 to 5,000 offspring. They can have four litters a year.
Dogs: in Malaysia fare much worse, though the cruelty and neglect in first/second world Singapore is a shocking shame still.
Sterilize and neuter - no other way to bring down the population. And none of that "I would like her to have at least a first litter" which leaves 5 puppies or kittens to be placed in uncertain homes.
Noah's Ark does such a brilliant job with 800+ abused/abandoned dogs and 500+ cats [one of whom had only one eye and no tail from vicious cruelty - she lived in fear till rescued and died at least in a peaceful haven]. The SPCA in Johor has no funds for a shelter and no funds generally: and there is so much to be done.
It is not kindness but cruelty to have cats and dogs 'roaming free' .. AP, your neighbour is irresponsible. First because cats hunt at night [bye bye night birdies, squirrels, tupais] and also because not all the other neighbours are going to try and ignore the menace but might resort to hurting or killing.
Noah's Ark is happy to arrange to sterilize strays for RM$50. But who has the heart to pay for even one stray?