Nexa, yea I read it a couple of months back. I am admitedly a little foggy on the details, but I do remember the gist of it.
You wrote: "because stealing cannot be good based on the contradictions such a statement implies"
But there are no contradictions. There is nothing logically invalid about a claim such as Stealing is good. Stefan argued in his book that stealing cannot be good because people would not be able to keep what they stole (since everyone would be stealing.) Yet this is utter nonsense. First of all, it doesnt even matter. "Stealing is good" does not provide a motivation for stealing. It doesnt say: "Stealing is good because it allows one to horde resources." It would make sense to simply say that stealing is good because it is fun to impose your will on others. Yet even if the goal was to horde resources, there is nothing inconsistent about this because it would simply be understood as saying "It is good to try to steal other people's resources while protecting your own." It does not say that if the oppertunity does not present itself to steal, that you are doing anything wrong. Just like the prescription for boiling water does not say anyone is wrong if there is no water available.
Consider one of the arguments I remember Stefan used against rape. Stefan says that if "rape is good" were valid, then given a room with two people, and one overpowers the other, the one getting raped cannot do good, which somehow makes the theory inconsistent. Utter nonsense... The theory is only a prescription, it is saying that one should try to rape. If one cannot acomplish the task, they are not wrong.
Now, another concern that Vichy brought up is: Who says that moral theories have to be universal and consistent across the category of humans? If I took over America and made rules such as: "It is good for Leo to take your things but it is bad for you to take Leo's things." What makes you say that there is something invalid here? The fact that people have similar natures? This fact does not logically imply anything about morality though. No where in the fact that humans are similar is it logically implied that humans should treat each other a certain way. You cannot get past this objection. If I say I should steal from you and you answer that I am wrong because me and you are similar, I will look at you like an idiot. I will ask, what does one thing have to do with the other? I am also similar to a rock, we are both made of matter, and yet you would not say I should treat the rock a certain way would you? If I said "Throwing rocks is good" would you say "No its not because you are both made of matter!" ???
There is nothing inconsistent about "It is good for Leo to take your things but it is bad for you to take Leo's things" because Leo is different from you. Leo is a different category of object than you, and such a theory would simply be claiming that this category of object (Leo) should steal while all other objects under the category of humans should not. To assume, as you do, that all normative claims must be consistent and universal for all members of the category "human" is totally arbitrary. Why can I not say that all normative claims relevant to Leo must only be consistent and universal for the members of the category "Leo." In this case "It is good for Leo to steal" is totally consistent and universal. And why can I not say that all normative claims relevant to all non-Leo humans must be consistent and universal, such as "It is bad for non-Leo humans to steal from Leo." This too is perfectly consistent and universal. What is happening is that you guys just arbitrarily assume that being human is some kind of reason for consistent and universal normative consideration. Well, unless you give me some reasons for this assumptions, than I must remind you that it is in fact, merely an arbitrary assumption.
BUT! Even setting all of those objections aside, even if we assumed that all normative claims all had to be universal and consistent accross all humans, your analysis of moral theories is severely flawed. There is nothing inconsistent about taxes and stealing, because, at least people in my society define taxes and stealing as two seperate actions. Taxes is not stealing. Nor is killing on a battlefield murder. You can shift the defenitions to your likeing such that you force them to be inconsistent, but then your analysis is no longer releveant to my society.