It takes a LOT more to mess up an animal's (bred over millions of years) resistance to the elements than a few years indoors. To respect any creature is to appreciate it for what it is. And a cat - timid or brave, playful or reclusive - is, first and foremost, a cat.
Same with a dog, a goldfish, etc.
Regarding your specific situation, perhaps you and your parents can come to a compromise? If you're concerned that your cat isn't properly acclimated to spending a night out in the cold (and it is, but regardless)... maybe you can start with an hour a night, then 2 hours, then 3, etc? Eventually you may be comfortable with it sleeping outside at night. But whatever happens, good luck and I hope you can all reach a common decision. Dealing with parents when one becomes an adult is a whole other dynamic.