Well Alan, I personally agree with you that domestic cats, especially in an urban setting, should not be left wandering around outdoors.
I think at the heart of the matter is that people who are not animal people tend to treat pets as disposable. I believe that is why so many cats end up feral. People get fed up with them, and away they go.
I feel bad for the wandering kitties in our neighbourhood - there are a lot of Coyotes and Foxes also wandering around and a cat is a great size for a snack.
I think that many people underestimate just how much work having a pet really is. They also underestimate the cost and are shocked an appalled when they find out.
I like the Trap/neuter programs because at least those cats will not be reproducing more.
I really wish people would not let their cats wander. It never ends well.