Fraser, you are obviously a responsible cat owner. Not a surprise, you seem to do just about everything right.
My definition of a feral cat is one that is living without being intentionally fed or sheltered by a human. In urban environments they are often called alley cats. They are not socialized to humans, though in some cases they can be. They are relatively infrequent in undeveloped areas because there are more predators and food sources are more difficult. Here in North America the most common cat eaters are coyotes, bobcats and some species of hawks and owls. These feral cats also exist in suburban environments, adapting to sheds, stoops, stored cars and other structures for shelter and dining on pet food intended for dogs and tame cats, as well as vermin, trash, small birds and anything else they find or can catch. If you haven't seen one of these you either aren't looking very hard, or didn't recognize what you saw. A prominent blogging veterinarian here in the US is fervently against killing stray and feral cats, but recommends capture, spaying and release as a way to allow these cats to "live their natural lives" while bringing the problem gradually under control. I know of very few places where there is enough effort put into this to actually cause a population decline.
Liking or not liking cats is a personal preference. I don't find the rewards match the effort, but I can easily see that others feel differently. My personal preferences are buttressed by significant allergies to the critters. Not surprisingly you often find that among the most fervent cat lovers are children. They get the benefits of cat ownership while mom and dad often deal with all the downsides (food, litterboxes, furniture repairs and vet bills to name a few).
I haven't actually killed or harmed a cat, but do haze them regularly to attempt to keep them away from my property. But I continue to be irritated by cat people who blithely ignore or dismiss complaints about the critters that they foist on the area. If the critter would not be there without your actions it is difficult to argue that there is no responsibility. To me it is like someone playing loud music saying that sound travels in all directions. It is physics and nothing they can do anything about.