The decision whether let let cats out is such an individual one and also depends on the nature of the cats.
I have two - Alfie is a big, neutered, male who came to me when he was just under 1 year old. He had been used to going out and pretty much climbs the walls if he has to be kept in for any reason. He likes to go out 'untin' and is good at it too (he has had 3 squirrels in the past couple of years).He would be a match for any fox that was daft enough to have a go! His need to go out over-rides my desire to keep him safe.
My second, Sky, is a little girl who came to us after a few months in RSPCA. She used to go out but was very ill last year and has been left with some balance problems. That, added to the facts that she is very small (2.5kg fully grown) and doesn't mither to go out, is enough for me to keep her inside, although OH is far from happy with this.
Neither of mine wear collars - Alfie simply won't keep one on, Sky is so scaredy that I cannot get a collar on without a great deal of stress (which is not worth it as she doesn't go out). They are both chipped, of course.