This was in response to a dude on philosophy forum.
First, I’d like to start this mini exposition by arguing that the consequence of no ethics is much deeper than is usually appreciated.
Not abiding by any ethic means making absolutely no should statements (that aren’t conditional), implicitly, explicitly, in the mind or elsewhere. Statements like "I should drink if I intend to live" would still be allowed, these are conditional, but as soon as the statement "I should intend to live" is made the person is now operating under an ethical system with at least one principle. And without any statements of the second form, statements of the first form are just useless commentary (though even so, conditional should statements are difficult to interpret as preferences: is the statement “I should walk out the door if I want to leave the room†a preference?†so this could be added to my criticism of preference based ethics below). If humans have free will, then denying all ethical statements, as in making no "I should" statements (including statements such as "I should believe, operate under, expound, or otherwise hold that no should statements are justifiable†) results in arbitrary action. If all people suddenly didn’t operate under any ethic, we’d all be pretty much dead in a day or two (no one would be able to assume things like "I shouldn’t stab myself in the face, jump off a building, smash my head into this wall etc". By coincidence some might live a bit longer (no one would be able to assume they shouldn’t drink water, cloth themselves, etc. however, they couldn’t, while remaining intellectually honest, which they also can’t justify doing, choose such things purposefully at any given moment over anything else they might do, such as drown, starve, roll around in a ball etc.).
Total randomness in action is the consequence of assuming no should statements are justifiable. That is if we have free will; if we don’t then it is still possible to claim "I cannot do anything but what I do, and this happens to be somewhat coherent", but all ethical theories, in the normal sense of the word, presuppose freewill, and so I assume the OP assumes we have some degree of free will. But even so, I for one am as unable to deny my free will as I am able to deny what I perceive or that something exists, and so have never felt a need prove I have free will; however, I do not think it would be possible to prove it to anyone but myself in any case.
Statements like "I should at least act in a coherent way", "I shouldn’t contradict myself", "I should drink water today if I can", all in themselves and in any combination form an ethical theory. It is actually surprising how many ethical statements people, that deny any ethics can be justified, make in a day. For an ethical theory, to be an ethical theory, need not be complete (resolve what to do in all situations), it need only to make at least one “I should …†statement and the person is operating under an ethic. It should be noted that the statement "there is no justifiable complete ethical theory" and the statement "there is no justifiable ethical theory" are not the same.
Interpreting all should statements as preferences or prescription doesn’t work in my opinion. One would still have to make the statement "I should do what I prefer". But even if there was a way around this, one would still need a method for deciding things when preferences conflict. "A maximizing of satisfaction of preferences over my life" approach is possible in theory, but in practice it is impossible to know what one’s preferences, which by definition are fundamentally arbitrary, will be in the next second, minute, year etc. The situation one is left with is "how do I know that pursuing my preferences now won’t exclude far greater preferences in the future". The theory also falls apart as soon as one doubts oneself in anyway. As soon as one raises the question "Is this really what I prefer" the theory needs a more fundamental theory to derive true or non-malleable preferences, which cannot in itself be based on preferences; and clearly, if one finds such a theory one "should" (if one wishes to justify preferences) follow it, which in itself can’t be interpreted as a preference; so the only way for the theory to work, if preferences become doubted, is to make should statements which aren’t preferences.
And doubting preferences I think is a foregone conclusion; the only way to escape this last criticism is if one never regrets any preference. As soon as one regrets preferences one either has to predict all future states of mind, which is impossible, or try to determine "what preferences should be followed, and what preferences shouldn’t". Or, one has to go for a search for "one’s true preferences", but this also has problems: is this search for true preferences a preference itself, or is one making the non preference interpreted statement "I should find my true preferences"? how would one determine if one’s found one’s true preferences (what would be not doubtable about them)? How does one even know one has “true preferences†. I could go on, but I think anyone that actually imagines this search will see that it has many problems, and I have never heard anyone argue this line; usually the preference/prescriptionist also embraces our total freedom to decide what we do.
In general, any preference/prescriptive based proponent is at least stating "I should hold this theory?" otherwise they are stating "well, it’s my preference to believe the preference ethics today, tomorrow maybe I’ll have a different preference" which is certainly not my interpretation of the proponents of these ideas. Though this isn’t a complete criticism, just pointing out enough to at least show that these theories cannot function in the simple form they are usually presented in. And after all this there is still the question of "is raping babies really justified if it’s someone’s preference?" That kidnapping a baby would be good in so far as it is useful for fulfilling the desire or reaching the goal of raping babies. So even if a theory avoided all the previous criticism, it would have to praise the efficient baby raper: "I like chocolate ... other people like raping babies. What’s the big deal? It could very well be me in a couple of years. Remember how I didn’t like broccoli". Or the theory must go on to claim there are limits of human freedom (that we are somehow barred from having this preference), but unless people are actually barred, which doesn’t seem to be the case, then the theory ends up trying to define the acceptable preferences, desires, goals and the non-acceptable and this reduces to an infringement on the sense of freedom and an absolute ethical theory, both of which avoiding was the point of the theory to begin with.
Back to more promising lines. Probably the first ethical principle each philosopher holds is coherence. I shouldn’t contradict myself or act in contradictory ways, if I find a contradiction in my ideas or actions I should try to resolve it. If you agree with this principle, contemplate why? And whether you hold it because it has some sort of innate value or some other constant value ... or whether you just happen to prefer it for the time being? Furthermore, do you think all people should try to avoid contradiction in their ideas and actions? If you find it is not a preference, but a principle you should try to adhere to regardless of culture, background etc, then you are not a preference/prescriptionist or ethical nihilist, but something else. If you think everyone should try to avoid contradiction in ideas and action if they can, you are an absolutist. You may not have a complete ethical theory, but you hold a universal principle.
Now I may at this point try to convince you of my ethical theory, but I do not think there is any need. Why did you make this post? If not to search for some truth?
If you encounter a situation where you cannot make or are not satisfied with a decision based on trying to find as much truth as you can, let me know, for I have as of yet encountered no such situation. Nor have I found a choice to make between things that both lead to a maximum of truth, that I am unsatisfied with a fundamentally arbitrary justification of one over the other.
I’m also not a big fan of the simple approach. It took me a lot of effort to figure out how to play guitar well, the math that I know, how to march and camp efficiently, how to read well, etc. why should I assume figuring out what I should do in general will be simple and easy? Unfortunately it makes for long low impact posts. However, I only have one last thing to say, and that is a lot of error stems from a confusion of “ethics†with “justice†. Philosophy today defines ethics as the pursuit of what one should do, and the study of should statements in general, and so essentially everything anyone does falls under ethics (they either think they should do what they do, or they think they should do something else, regardless of whether they’ve concluded what that thing is or not, but do what they do anyway for the time being). Justice on the other hand is a different and more limited matter in human affairs. Making the assumption that a theory of ethics would be equivalent to a theory of justice, and vice versa, leads, as far as I can see to much of the confusion and error found within ethics and political discussions.