Figured it'd be just as good to keep the questions to one thread, so I'm going to answer Stefan's question form the other thread here aswell.
I'm somewhat new to the whole ethical nihilism, of course, and most of these thoughts I've never actually written down before. So please have patience!
Stefan Molyneux:
So -- what you're saying is that it is universally preferable for theories to be logical?
Also, UPB in no way proves that anything is "objectively bad" - what
it does prove is that the logical proposition that "rape is good" is
false.
In the same way, the scientific method does not prove that not using
the scientific method is "objectively bad." It does prove, however,
that if you do not use the scientific method, your statements or
conclusions have no truth value.
Stefan Molyneux:
If I understand you correctly, you are saying that:
- There exists no universally preferable behavior ( Which I would agree with)
- There does exist a standard of truth that is universal and objective (" What you believe is wrong.")
- It is universally preferable for people to speak the truth rather than falsehoods or error.
- Thus it is universally preferable that people recognize that there is no such thing as universally preferable behavior.
- If someone argues for universally preferable behavior, then, they are incorrect, because it is universally preferable for people to speak the truth rather than falsehood.
- In this way, universally preferable behavior is invoked to oppose universally preferable behavior.
I am not quite sure how this is not a self detonating argument, but perhaps you can help me out?
Right, I might have been somewhat unclear with my usage of the term "UPB". So let's start over a bit and define our terms, and maybe we can finally understand eachother. 
So, from what I understand, UPB is just like the Scientific Method - it is a method/framework/whatever from which to derive certain truths about the world. Now, for the sake of the discussion, let's assume this is correct; let's assume we can use UPB/SciMeth to prove or disprove claims about the objective reality.
Now, if someone claims that "gravity exists objectively", we can now use the SciMeth in order to test this statement and see if it is true or false. Using the SciMeth, we find that yes, gravity does exist objectively! What does this mean then? Well, it means that the statement "gravity does not exist in reality" is false/wrong/untrue.
When it comes to morals, I'm sure we can define it as 'what acts people find right/good and wrong/evil'. Just to clarify, morals absolutely exist in reality, just like taste, smell, and these kind of things do. Everyone has them. For me, I find murder immoral. I'm sure everyone here does too.
This, for me, means that I would call a murderer "evil", and it means that I personally would find his action wrong.
Now, the question we're faced with, is whether or not we can say that I am "wrong" for believing what I do about the act of murder, and if what I believe is right or wrong. This is where I start to have problems.
Can we say that someone is "wrong" for believing gravity doesn't exist? What he believes is objectively false, of course (according to the SciMeth), but can the act of believing in something false in and of itself be objectively wrong? I do not see how it can, at least not "wrong" in the sense that "gravity doesn't exist" is wrong. "Gravity doesn't exist" is wrong, because it makes a statement about reality that isn't real. The abstract idea deviates from reality - the idea cannot be put into practice, so to say. "Gravity exists" can be put into practice, and is therefor an objective truth.
However, the act of believing the idea cannot deviate from reality, since the act itself is real. Murder, too, is an act that is very real. Therefor, we cannot use "wrong" in the same sense when saying "murder is wrong" that we are when saying that "the idea that gravity doesn't exist is wrong". So we'll need to rephrase it somehow, maybe into saying "the idea that murder is moral is wrong".
So let's assume I myself find murder to be a moral action. What the claim "the idea that murder is moral, is wrong" means, is that I myself am not wrong in believing what I believe, but my idea supposedly is wrong. So apparently, "murder is moral" is objectively false (according to the claim "the idea that murder is moral, is wrong"). However, this assumes that we can say that moral ideas are "objectively right" or "objectively wrong". Here, the real problems for me begin.
You claim that we can test to see if the idea "murder is moral" is right or wrong, like we can test to see if the idea "gravity exists" is right or wrong. Basically, what you seem to be saying is that there exists some kind of objective statement in the claim "murder is moral". I don't see how this is possible. "murder is moral" is, after all, just a statement of personal preference, just like "ice-cream tastes good" is. Morals, like taste, only exist inside people's minds.
There exists no morals "out there" in the universe. When making the claim "murder is objectively immoral", the idea is that there exists an objective morality (just like there exists an objective gravity), and ideas that go against this morality (like "murder is good") is somehow wrong/false/untrue (like "gravity doesn't exist" is).
So, what ethical nihilists say, is basically that when it comes to morals, it is impossible to try and make objective claims. "Murder is moral" cannot be objectively true, nor objectively false, for the simple reason that the idea is not making a statement about objective reality. In short, "Murder is moral" is just a personal preference, not a statement about reality.
However, the statement "murder is objectively immoral" is a statement about objective reality, and can therefor be proven or disproven. It requires that there is an objective standard to which we can compare the morals, the existstence of which I have yet to see proven.
What happens in the UPB-book is that you, Stefan, take on different moral ideas and test them for logical consistency and whatnot, however there is absolutely no proof for the existence of any "objective morals". What I mean is, you test "murder is moral" for inconsistency, but you do not test and prove the claim "there objectively exists a moral standard to which we can compare our morals and see if they are right or wrong".
So when I go out and murder someone, yes, you might rightly call me an illogical, inconstistent asshole. But how can you say that my act is somehow "objectively wrong" or "objectively evil"?
What says there is some "standard" existing objectively which tells certain atoms what to do and what not to do? If it exists and does not speak, what is its importance? Why seek it?
Oh, and to quickly cover "but the acts are imposed on other people"-thingy, this still does not prove that the acts in and of themselves must either be "objectively right/good" or "objectively wrong/evil".
Reading through all this made me realise these discussions are very frigging hard to type out, heck, only this little bit gave me a headache. I'd pass away writing a book like UPB, or anything philosofical work that covers metaphysics, epistemology, or something like that..
Hopefully someone will understand something, and post a nice reply which totally destroys my arguments and changes the way I think - again! 