In response to a number of blogs and articles which claim that there is no material reason to be good, and the claim that morality is a holdover from religion, there are a number of responses that have stood the test of time. Plato's Euthyphro is one, in which it is pointed out that if goodness is based upon the opinion of higher beings, it is still merely a matter of whim, and that their must be a standard higher even than the gods by which the good is judged. It has also been observed that the ethics of religions themselves evolve through co-opting the ethical advances of the societies of which they are a part. Slavery is a good example: there is nothing in the Bible against it, and yet all of Western civilization has come to the conclusion that it is wrong. The same is now happening with regard to women's rights and gay rights. These changes are imposed upon religions from without. They must come from elsewhere. So what is the root of human goodness, and the driving force behind ethical reasoning?
As any society advances and grows in numbers, it is faced with problems related to higher populations making greater demands upon limited resources, and higher population densities which must be managed so that their living space (ultimately, cities) do not become toxic waste dumps. The solution to these problems is technological; unless these problems are solved, high mortality rates will keep population numbers low. Technology is required both to allow for lower mortality and to cope with the greater numbers made possible by it. This growth of technology is a growth in knowledge, and to deal with this the society must pursue increasing specialization. We need doctors in multiple fields, mechanics, plumbers, carpenters, programmers, engineers (again in multiple fields), policemen, city planners, accountants, and so on.
Now all of these specializations create informational disparity. If I bring a car in to have it fixed, I probably have no idea what needs to be done, the cost of the parts, the work involved, or the true cost of all of it. I have to trust that the mechanic is not cheating me. There is competition, of course, but it is never perfect. I may have to go to a particular shop who specializes in my make of car. I can, of course, do research on this and become something of an expert on the car I drive. But I have limited time; I cannot master all things, I must trust specialists in their area of specialization. Indeed, in order for an advanced civilization to function, it must operate on a basis of trust. Otherwise the advanced civilization that we now enjoy would become impossible. Life without trust is nasty, short, and brutish.
Consider societies where this trust does not exist. In ours, we take something from the shelf, and pay the sticker price. In societies that do not have this level of trust, they haggle over every price. But haggling takes time and expertise that could be better spent on our own areas of specialization. As a result, societies that haggle are poor.
Trust requires honesty. Salesmanship can only work if the claims made by salesmen are largely true. Every lie, every cheat, every act of sleaze costs us all. The liar is a freeloader. He is exploiting the trust that the rest of us work hard to establish for a quick payoff. He thinks he is getting away with it, but he isn't. First, of course, he is eroding the trust that our society needs to maintain itself. In this way, he is like the coyote in the Warner Brothers cartoons, sawing away at the plank that is supporting him over the abyss. But it goes further than that. If he brags to his friends about what he has done--and he will, to seek approval and justification for his actions--his friends will react in one of two ways. They may be encouraged to follow suit, thus eroding the foundation of society still further. Or, they may smile and nod, and realize that their friend is not to be trusted. And they will warn others, and for his short term gains, this man will pay a hundredfold.
Few sins can survive the light of truth. Honesty is the universal acid that burns all evil. War and tyranny require a bodyguard of lies. And honesty is required to sustain us in the style to which we have become accustomed; the style to which everyone in the world aspires to. So, to live a good life, you must be honest. And to be honest, you must be good.
Morality, it turns out, is required by the human situation. It is inescapable, if you wish to live in a world worth living in.
But some will say that that does not matter, that human concerns for comfort and prosperity are irrelevant, and that what is good might require mass human suffering. This is the morality of abstract principle. This is the morality of the bolsheviks and the Reich. Francis Fukuyama said that there are some mistakes you need a PhD to make. There are some mistakes you need to think too much, and feel too little, to make.
Let me take you on a thought experiment. I take your index finger and place it on a slab of granite, and with the other hand I take a three pound sledge, and I crush the end of your finger. Not enough to sever it, but enough to reduce the last two bones to razor sharp fragments of serrated bone, exploding the joint, permeating all the flesh--flesh, I might point out, which is so completely permeated with nerve endings that they can detect brail points a couple of millimetres apart, and all of these are now screaming a single signal of pain. The pain would be so intense that, if you were subject to cardiac weakness, it might well kill you. But at the very least, it will annihilate you. "Cogito ergo sum", Descartes said, but there would be no cogito, and no sum. You would cease to exist before a storm of raw qualia that would burn away all consciousness of everything except for that finger. You would become simply an animal in pain.
At that moment, if I were to ask you, "Is this good?", you would answer "No!" And you would know the truth of that with every fiber of your being. This is what a fact feels like.
Hume said that you cannot get an ought from an is. But what if the primal ought is an is? I suspect that all morality begins with a baby bumping his head, stubbing his toe, mashing or burning his finger, and screaming incoherently to the world, "THIS IS WRONG!" Psychopaths never connect their own pain to others, but normal people will, and will understand that unnecessary pain, particularly extraordinary pain, is always wrong, and not just for them, but for everyone.
And from this, all the rest follows.