My view is cats do not need to go outside.
Sorry, I don't agree with that, given the option most cats would choose access to outdoors, it is part of their make up, its hardwired into their brains. Mine all have access to the garden, one part comletely enclosed for nighttime, the rest of the garden isnt completely enclosed, and they have access to it the rest of the time.
My ginger mog, Harry has always gone out of the garden (he's 11 now) and he wouldnt have it any other way, and nor would I. He wouldnt be Harry if I restricted him in any way, even to just the garden itself. On the other hand, I have Elsa who at 20 is happy to stay indoors now, her choice, despite being an intrepid hunter in her younger days! Persians Zeta and Jasper who came to live here in March are also very different, Zeta potters about the garden and has only once made the mistake of getting stuck up on the neighbours fruitcage! Jasper on the other hand, clambers over fences 6ft high, and takes himself off on a walkabout most days! You can't just have a blanket statement that says 'cats don't need to go outside' Some do, some don't.
As to harnesses, well I've never tried them, but back in the 70s hubbie and me used to take our black mogs Sophie and Schweppes out for walks in the country on collar and lead (not recommended I know!) and they used to love it, but then they had free access to the garden and surrounds anyway. I agree that it wouldnt be fair to take cats out on a harness that werent going to be allowed to have outdoor access at other times.