Mine are indoors only because they are ex-Feral, and the chances are that if they go out they may well go Feral again. Also, I'm paranoid about cars, accidents, poisoning (intentional and accidental), evil cat killers, the enormous ginger & white local Tom that beats up all the cats in the street etc. In many countries like the USA the majority of cats are kept indoor only. You also have cats with conditions like FIV who need to be kept in.
However there is the argument that cats need their outside time as it's much more natural for them, and hunting & killing prey is an integral part of being a cat.
Your friend who puts her cat out all night is waaay behind the times. Cats are actually crepuscular (love that word!) which means they hunt at dawn & dusk NOT particularly overnight. They are more likely to come to harm overnight outdoors, and should never be locked out if avoidable in case of problems.
Being indoor cats, mine only get flea'd & wormed annually as a precaution (unless of course I see anything); I do pet an awful lot of other cats and dogs so I prefer to be safe rather than sorry 
. They get their annual MoT partly because of the vaccination, and partly because cats are very good at hiding anything that's wrong with them. It's also useful to have knowledgeable eyes on them who don't see them regularly, as people who see a pet frequently may not notice changes as well.
I'm not sure where they got the idea of keeping kittens in cages from, unless they had the kind of household where they couldn't be sure of keeping them in. Kittens should never go out until they have been vaccinated, microchipped & neutered/spayed.