Troy is certainly right, this is a personal decision that has to be based on many things that vary from pet owner to pet owner. In most of urban and suburban America, it is likely that most cats are safer inside. And most danger is created by man, as it is with all the creatures of the earth.

But factors vary within the cats themselves, too. Not all cats are avid hunters, and the fact that they can't chase mice and birds is no great loss. Not all of them climb trees and play hide and seek. And by nature cats are solitary animals, so the fact that they can't meet the neighbors would probably not be a significant matter to them, either. Also, many of these activities can be simulated or experiences indoors - multicat household cats certainly are socialized, and many and varied toys make for good "mouse" chases, and some good furniture, cat or people, can be easily climbed.

Many indoor/outdoor cats live through their teens, and many indoor cats die kittens.

It is a personal decision, and certainly no one's opinion is nonsense for them.