You're making a mistake, in assuming that ethical systems are intended to do what you think they're intended to do. I'm going to make some complete unsubstantiated claims; you can evaluate them for yourself.

Point 1: The ethical systems aren't designed to be followed by the people you're talking to.

Normal people operate by internal guidance through implicit and internal ethics, primarily guilt; ethics are largely and -deliberately- a rationalization game. That's not an accident. Being a functional person means being able to manipulate the ethical system as necessary, and justify the actions you would have taken anyways.

Point 2: The ethical systems aren't just there to be followed, they're there to see who follows them.

People who -do- need the ethical systems are, from a social perspective, dangerous and damaged. Ethical systems are ultimately a fallback for these kinds of people, but also a marker; "normal" people don't -need- ethics. As a rule of thumb, anybody who has strict adherence to a code of ethics is some variant of sociopath. And also as a rule of thumb, some mechanism of taking advantage of these people, who can't know any better, is going to be built into these ethical systems. It will generally take some form akin to "altruism", and is most recognizable when ethical behavior begins to be labeled as selfishness, such as variants of Buddhism where personal enlightenment is treated as selfish, or Comtean altruism.

Point 3: The ethical systems are designed to be flexible

People who have internal ethical systems -do- need something to deal with situations which have no ethical solutions, but nonetheless are necessary to solve. Ethical systems which don't permit considerable flexibility in dealing with these situations aren't useful. But because of sociopaths, who still need ethical systems to be kept in line, you can't just permit anything. This is where contradiction is useful; you can use mutually exclusive rules to justify whatever action you need to take, without worrying about any ordinary crazy person using the same contradictions to their advantage, since they're trying to follow all the rules all the time.

Point 4: Ethical systems were invented by monkeys trying to out-monkey other monkeys

Finally, ethical systems provide a framework by which people can assert or prove their superiority, thereby improving their perceived social rank (what, you think most people here are arguing with an interest in actually getting the right answer?). A good ethical framework needs to provide room for disagreement; ambiguity and contradiction are useful here, as well, especially because a large point of ethical systems is to provide a framework to justify whatever action you happened to take. This is enhanced by perceptions of the ethical framework itself, which is why mathematicians will tend to claim utilitarianism is a great ethical system, in spite of it being a perfectly ambiguous "ethical system"; it has a superficially mathematical rigor to it, so appears more scientific, and lends itself to mathematics-based arguments.

See all the monkeys correcting you on trivial issues? Raising meaningless points that contribute nothing to anybody's understanding of anything while giving them a basis to prove their intelligence in thinking about things you hadn't considered? They're just trying to elevate their social status, here measured by karma points. On a site called Less Wrong, descended from a site called Overcoming Bias, the vast majority of interactions are still ultimately driven by an unconscious bias for social status. Although I admit the quality of the monkey-games here is at times somewhat better than elsewhere.

If you want an ethical system that is actually intended to be followed as-is, try Objectivism. There may be other ethical systems designed for sociopaths, but as a rule, most ethical systems are ultimately designed to take advantage of the people who actually try to follow them, as opposed to pay lip service to them.