Why not just kill cats?

I can think of three understandable reasons for being angry at cats: cats pee and poop in flower beds; cats leave tracks on cars; cats decimate wildlife. While it's true that cat owners bear all of the responsibility for these problems, it's their cats who are vulnerable to retaliation, and I consider it probable that people who dump cats' mutilated remains in their owner's yards (see last post) are trying to send a message to everyone who has outdoor cats. 

When I moved into this creek-side neighborhood 28 years ago, it contained an abundance of squirrels, raccoons, nutria, songbirds, opossums, non-poisonous snakes, and waterfowl. Roughly ten years ago, multiple neighbors got multiple outdoor cats (one neighbor had eleven), and I watched in horror as those cats decimated the wildlife. Thanks to irresponsible cat owners, the birds that lay their eggs in the high grass across the street are all gone as are the non-migratory waterfowl (dead migratory birds being replenished by new arrivals). I went from finding several garter snakes and king snakes a year in my yard to only seeing one in the past eight years. Even the nutria, opossums, and raccoons have been hard hit, presumably because cats target their young.

I got cat shit on my hands so often while working in my flower beds (buried cat shit blends in nicely with dirt clods) that I finally took to wearing plastic gloves. Then there were cat tracks on my car and the trauma experienced by my own cats every time they see outdoor cats in their yard. People who have outdoor cats claim that I should take all this in stride. Their arguments take six forms: (1) It's inhumane to keep cats indoors*; (2) I really need to lighten-up about cat shit in my flower beds and cat tracks on my car; (3) Cats are natural predators, so it's only natural that the local wildlife be decimated by a superabundance of recreational killers; (4) Cats only "cull" old and weak birds, reptiles, amphibians, and mammals; (5) Numerous studies and my own abundant observations notwithstanding, cats are such sorry hunters that they rarely kill anything; (6) Finally, there are those whose poor self-image cause them to take pride in their cats' hunting prowess.

If I had previously disliked cats or was indifferent to them, what I have witnessed in this neighborhood would have turned me into a bonafide cat hater. But is killing cats the solution? Surely, a dead cat can't harm wildlife or poop in flower beds, but would the benefits of killing cats outweigh the downsides? Unless it's done on a large scale (as by the government in Australia**), I can think of several reasons why it wouldn't, and I'm going to devote the rest of this post to arguments I might offer someone who was thinking of becoming a cat killer due to legitimate concerns regarding the damage done by outdoor cats:

(1) There being so many ways to bring good into the world, is one that brings death to cats, grief to their owners, outrage to the community, and stress to yourself, worthy of your time and talent?
(2) Would you want your child to follow your example?
(3) How much would you worry about being caught, and if caught would the satisfaction of having killed however many cats justify the resultant hatred, job loss, criminal prosecution, and abandonment by friends? 
(4) Studies show that many cats seldom if ever hunt, and still others are too old to hunt (cats begin to decline, mentally and physically, at age seven), which means that the bulk of the killing being done by a limited number of cats. How, then, would you know which cats to target? 
 (5) There's a saying that goes: Behave as if your actions were to become universal law. If you wouldn't approve of all of the world's people using unilateral violence to solve problems, would not your use of violence suggest egotism and arrogance?
(6) Would you be saddened by the need to erect a lifelong wall of secrecy between yourself and others, a wall consisting of the times you hid in the shrubbery on dark nights slaughtering cats? Or would you boast of your killings to everyone you trusted, only who could you trust, not just today, but next year when you and they had an argument? 
(7) When you caress a loved one, would the memory of the terror and death that your hands inflicted put a distance between you? 
(8) What would you do if an innocent person was openly accused, possibly assaulted, and had his property vandalized?
(9) If people came to surmise that an environmentalist was responsible for the killings, how would you feel about their resultant hatred of all environmentalists and their possible targeting of a specific environmentalist? 
(10) How many cats do you plan on killing--one, three, a hundred, as many as possible every weekend for years--possibly branching out from your neighborhood to other neighborhoods and even to other towns? 
(11) When you die, would your unknowing loved ones wrongly praise you as having been a man whose life was a blessing to all who knew him, who loved children and animals, and who devoted himself to making the world safer and kinder for all its inhabitants?

* If your cat spends much of its time alone, and you don't provide him or her with abundant opportunities for exercise and stimulation, this is true, but then you shouldn't have a cat.