The difference in walking a dog on a leash and walking a cat on a leash: when walking a cat, you must go where the cat wants to go. You can't expect to lead him steadily down the sidewalk. Instead, your walk will be 5 paces north, 10 paces southwest, 2 paces east, 2 paces west, 2 paces east, 8 paces north ~ and insert looong sniffing pauses in between all of those!
Like spanishliz, I had a rescue cat years ago that had been declawed, so could not go outside. And he was dying to -- constantly trying to get out the door. So I got him a harness, and at first he would just lie there, but once he realized it would allow him to explore outside, he loved it!
I know that many cats live long, happy lives outside, but it's extremely dependent on the neighborhood. It seems cruel if one lives on a busy street to get a cat and let it outside, knowing the chances are high that the cat won't live long. I've moved several times over the last two decades, and without knowing what sort of neighborhood might figure in my next home, I've found it better to let my cats get used to being inside. But I have built them a screened porch every place I've lived that had any sort of place feasible to do so ~ including the balcony of a city apartment building.
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"The greatness of a nation and its moral progress can be judged by the way its animals are treated." --Mahatma Gandhi