Seriously though, cats are not really exclusive to the problems. Dogs are just as bad too, and just as many feral dogs world-wide, and a lot of people leave them to free-roam in Australia I heard. However I am not sure on the legality of it since I am
not an Australian.
I don't know why urban people let their cats free-roam, yet keep their dogs on chain either, other than what the law says. I have seen some people chain their cat to the clotheline, and they don't leave the yard. I have seen dogs jump fences and climb trees via branches, so they have similar, albeit not the same, abilities as cats. Heck, in order to keep our dog within the yard, my family to make a 1 foot above-ground concrete foundation and an 8-feet fence ontop so he would not try to jump it since the dog figured out how to get out of all his collars and harnesses.
So the only real thing that can be done about the domesticated cats is to treat them the same as domesicated dogs. Feral cats and dogs are not going to go away, so there is not a whole lot people can do about it except for desexing them and removing portion off the streets and removing them from the countryside.
So what the difference between feeding a dog or a cat to a snake? No difference really, except for how people value them. Personally, I would not have a problem with using deceased cats or dogs if it doesn't cost a lot of money and time in order to do that -- or if I actually have something to feed them to. However it is not feasible to run such operation so breeder mice, rats and rabbits are better, even over the fancy varieties.
Even then... taking a pet and feeding it is wrong, even though some of us would like to do it... I know I would love to take that bloody parrot somewhere in the neighbourhood that keep annoying me at night and feed it to my dog.