Considering that conventional wisdom is seldom wise, however, it should come as no surprise to anyone that about 2,350 years ago, the ancient philosopher Socrates came up with the ultimate logical refutation of the idea that religious doctrine could be the source of any morality worth respecting. Why should this be the case? Well, because Socrates had the courage and the philosophical brilliance to ask a seemingly innocent question that has proved to be an absolute nightmare for theists ever since: Are right actions right because they are commanded by God, or are they commanded by God because they're right? Whichever horn of the dilemma you choose, you're probably toast either way :)
The philosophical insights derived from this simple question were beautifully expressed in Plato's early dialogue Euthyphro, and what Socrates shows is that Dostoevsky got it exactly backwards: he should have said that "only with God could anything be permitted" because if morality came from God, then God could arbitrarily command anything, like telling Abraham to sacrifice his son Isaac, not for any particularly important reason or for any greater good, but just for shit and giggles, just to see if he will do it.
You may object and say "Oh, but God wouldn't command something heinous like that." Why not? Because it's wrong? If you say yes, aren't you conceding the fact that morality is independent of God and that God is ultimately irrelevant to questions of morality and objective values since some things are wrong regardless of what God may say or think?
If you want to download a pdf version of this wonderful piece of classic literature and philosophy, click here.
Some people are clever enough to try to call the Euthyphro dilemma a false dilemma. They argue that there are more possible choices besides those allowed for by Socrates. They may argue, for instance, that goodness is part of God's essential nature, which is, by definition, to be benevolent, loving, merciful, etc., but this is just a different way of saying that God is good by definition, which is still the first horn of the dilemma, just dressed up and prettied up to look better, but it's still the same corpse beneath the dress.
But let's grant the theist his accusation of a false dilemma. Socrates could play the same game and corner the theist exactly into the same corner once again, as this hilarious cartoon shows:
And if you're confused about what the Euthyphro dialogue was all about, don't feel bad. Most people miss the point the first time around, but luckly for you, philosopher Louise Antony explains it with great clarity in this fascinating debate against theist philosopher William Lane Craig.