In 25 years, nine cats have come through my life, the first two for very short periods: Chinook died before she had a chance; Percy was a stray who came, and then went.
Then Shasta came into my life, and the real parade began. I could go into great detail, but won't. Shasta was over 21 when she died of old age; Gryphon and Nibs were into their teens, when they died of causes unrelated to the outdoors; Suzy is 4, Cindy and Fawn are 2.
Right. That's only 8. Samantha was Suzy's sister, and she disappeared when she was 11 months old. My heart breaks every time I think about her, and will forever. She was my Drama Queen. Somewhere I have a poem about Sam that I may get around to posting.
But, in my experience, she's the exception to the rule, including a lot of second-hand experience -- that of friends and family and their cats. So, while I chew my nails, pace the floor, and whatever else, when one of my kids stays out longer than expected, I won't deny them the experience that they clearly choose, and that seems to help them be more contented and peaceful.
That does not mean I think it's wrong to keep a cat in. As several people have already said perfectly eloquently, it's a matter of judging the particular situation and doing what you believe is right for YOUR cat.
Someone pointed out that this is a hot-button issue, and it most certainly is for me, because there have been times when I have felt attacked for my stance. In fact, a friendship that began with a common interest in cats, came apart (in part) because my friend's stance changed over time from enjoyment of my cats' escapades to a point where she could not even acknowledge the possibility that I, too, made my choices out of love for my critters. The issue has been costly for me, but I thought I'd try to add my perspective. I hope I've kept it sufficiently calm.