my mum lets children play in her backyard, as well as her cats. both know not to go too far, and that cars aren't for playing with. the most predetary animal in my parents neighbourhood is a hedgehog, and there are thankfully no weirdos about that we've met (small community) and not too many people around who are looking to steal a pair of slightly overweight middle aged non pedigree cats. they've had all their vacinations too. i feel that they're relatively safe, and that they're much happier free to be in the fresh air and sunshine than they would be if they weren't allowed out.
but owners, like parents, make their own choices, and do what seems best for their family, so i agree, each to their own.
obviously if i lived right next to a motorway, if my kids/cats were at a heightened risk of disease, if i knew that there were a lot of people in the area who weren't the friendliest, and if cats/kids had demonstrated poor judgment and decision making skills in the past, then letting my cats or kids out unattended would be foolish for me to do. but i don't have these issues, so i'm prepared to balance the -in my case very small- risk of something bad happening to those i care about, with the happiness that their experiences bring and the quality of life that going outside affords them.
if the risk was higher, i'd still probably take them out on a lead though (cats or kids, my mum had me on reigns as a child, lol), or find a way to make a large area of my garden as secure as was possible- to keep them safe, and keep danger out as much as i could. if things were that dangerous where my children or animals were, i'd probably do my damnednest to move, actually. (though i understand that if the whole country i lived in was unsafe, this'd perhaps be tricky, lol!). either way, i'd probably not choose to have cats, if having them meant that i'd need to confine them to the house perminantly- but like we both said, each to their own.