Unlike Tolstoy's, the style of Fyodor Dostoyevsky is a tad too turgid for my taste, so I confess that his Brothers Karamazov awaits my attention yet. Its most famous phrase, though, spoken by Ivan, one of those Brothers, is the subject of these remarks:
"If God does not exist, then everything is permitted."
That is, he said that if there is no God, then there are no rules to live by, no moral law we must follow; we can do whatever we want; morality and ethics are dead.
I'm a bit puzzled that he did not write it as "If God did not exist, then everything would be permitted" because he was clearly a theist and a Christian, so this condition would be to him hypothetical; but perhaps that was lost in translation.
The book appeared in 1880, and his dire prediction was fulfulled within a half century; the lapsed seminarian Josef Stalin arranged to starve eleven million Ukrainian farmers to death in the name of the Soviet State, and a little later the former choirboy Adolf Hitler liquidated six million people for the crime of being Jewish. No rules, no morality, everything was permitted. God having been taken out of the equation, humanity began to destroy itself.
I see two errors in Dostoyevsky's lament.
First, Stalin would never have had the power to commit those mass murders if he and his fellow thugs had not won the Bolshevik Revolution, and that revolt would not have happened if Russia had not lost the war against Austria and Germany, and that loss would not have occurred if the pious, religious and revered Czar of all the Russians had not let loose his army with instructions to kill Austrians in 1914; a grossly unethical decision compounded by his idiocy in doing so with an army ill-equipped for the job.
By entering that War for the trivial reason that Czar Nicholas wanted to prevent his rival Emperor in Vienna taking tighter control over Russia's ally Serbia following the assassination of the Crown Prince, he wrote a death warrant for himself, his family and for Christian Russia as it had existed for hundreds of years. Indeed, that one act of his did cause WW-1 to begin, for he knew full well that a Russo-Austrian conflict would, by treaty, bring in Germany and France; so we can lay at his door the 16 million deaths it caused. In turn, that first round was the primary (though not inevitable) cause of WW-2, and so of its 60+ million more deaths.
Did Nicholas pray to his God before deploying his army? Did he read Commandment #6? Did he consult his advisors, spiritual as well as temporal? Didn't his God reply, saying "Hang on a bit; there may be a better way"? Why not? So Dostoyevsky's premise that his society was moral because it was grounded in belief in a God who exists, was flat false. The Czar at least was already "doing what he wanted," regardless of ethical constraints. Governments usually do.
Second, his premise was false for another reason: good morals and ethics do not depend on the existence of God anyway; He is not the only possible source.
That one does have the virtue of simplicity, well suited to the job of telling kiddies in Sunday School why they ought to do right - ie, because God says so. End of argument - except that God cannot be proven to exist, and has not yet even been defined; but the kiddies won't pose those objections then.
There may be other bases, but the one that makes sense once we accept the axiom that each person owns his own life goes as follows, and will prevail in the coming zero government society: if you accept that axiom - an objective, demonstrable truth - then you have first a powerful rationale for not interfering in any way with anyone else's use of his own life; not by hurting him or her, nor by taking his stuff.
The same axiom brings a second powerful motive for good ethics: self respect. Your own life is your one, major asset. Therefore you will want to enhance and nurture that life, to enjoy it more and more. You find that the avoidance of bringing damage to others does in fact enhance it, by bringing you pleasure or satisfaction; even more, if you choose (without obligation, of course) to do someone else a favor of some kind, your own self-esteem is enhanced further yet.
It also brings the motive of preserving one's reputation; for that is also a key asset. We will, in the coming zero government society, succeed only to the degree that our reputation is sound, so that people can trust us.
Notice that these powerful motivators are pretty well opposite to the one driving Christian ethics: self-sacrifice. The principle there is that "Greater love hath no man than this, that a man lay down his life for his friends" (John 15:13.) But in rational ethics, the motive is to build or enhance life and its enjoyment, not to give it up.
Self interest, therefore, is the rational basis for ethics. It requires no assumptions about supernatural entities, it's right down to earth, and is enormously powerful. It can be practiced now, at once, and will come to full flower shortly, when the monstrous contradictor of self-ownership has evaporated for want of employees.
In one sense, Dostoyevsky's Ivan Karamazov was quite correct: absent God, everything is indeed permitted, nothing forbidden. Instead, each of us is entirely responsible for our own actions, and well motivated to conduct our lives so as to enhance them. Result: a society in which everyone's life is massively enhanced.