When you write utilitarianism, I assume it’s a typo?
On your first point: if by null system you mean no moral guidance whatsoever, so that you allow violence, I think this fails criterion (c) - it’s pretty dystopian in my view. Of course, that criterion specifies that the judge of whether the resulting society is dystopian is the theory’s proponent, so if you think that’s an acceptable society, fair enough, and you are right.
I do think libertarianism meets (b) - I think your propositions (no one has the right to inflict suffering on others...) is exactly what I am saying, I don’t think it’s a weak statement… why do you think so?
I think there may be some confusion though on how we define liberty—I use the term literally, so I do not accept that a rich person is more free than a poor person, for instance. So there can be no situation where you infringe on A’s liberty to increase B’s—unless A has already broken the moral code by physically harming B. For (2), this goes back to bootstrapping: because you have no right to harm others, people have a right to prevent you from doing so.
Re moral authority: actually both statements work—unless you can convince me of your moral authority’s existence, I will not accept it as a basis for morality, and so the point is moot. We need to ground our morality on facts that are accepted as facts by everyone sane (I know the definition of sane invites a lot of debate, but I am being a bit practical here!)
You are right that we have limited computational power, but this is a theoretical tool. I do not grant that a) is impossible—it can be achieved by either having a system that relies on a single principle (e.g. libertarianism) or one that relies on ordered principles, so that if two conflict in a particular scenario, you go with the highest ranking one.
On (b), insane people & postmodernists aside, I do think there are facts on which everyone agrees… and re the latter, I do not know how seriously I take their disagreements with objective facts given that I have yet to witness one jump out of Sokal’s window!
Yes, that’s what I mean about societal vs personal. A societal theory should be coercive, which is exactly why it must meet these criteria—otherwise, if it doesn’t meet (a) there will be situations where the theory will coerce you to perform two mutually exclusive actions, if it doesn’t meet (b) you won’t get people to agree to a covenant that allows for coercion and if it doesn’t meet (c), if you start coercively applying its principles, you will end up with a dystopia.