My priest and I were discussing this yesterday; we agreed -as most Orthodox Christians would- that Orthodoxy has no ethical theory as such.
Philosophical ethics today is in a crisis mode characterized more by Postmodern malaise than the now quaint Enlightenment pontifications of yesteryear about the advent of a "scientific ethics," which found its first major naysayer in the person of Friedrich Nietzsche (cf. Nietzsche, Beyond Good and Evil). Bonhoeffer actually thought Nietzsche did Christianity a service of great value in debunking the Enlightenment mentality of "scientific ethics" whether of duty, utility, sentiment, etc. Bonhoeffer opined that it was the fruit of *knowledge of good* as well as knowledge of evil which was forbidden to Adam in the Garden. For this reason he concluded that the notion of Aquinas, that God created us with *knowledge of the good* as a part of the Imago Dei, was the devil's lie. It is arguable -many do argue it- that the grounding of ethics (e.g. Natural Law) and theology (e.g. Natural Theology) on the sand of discursive reason led straight to the death of God and ethics, with as its ultimate consequence the death of man -though this God who "died" (culturally/intellectually in the academic West) was the God of the philosophers rather than the living God of Abraham, to use Pascal's phrase.
On the other hand, scripture tells us that God places his law into our heart and that we are without excuse. Does this contradict what Genesis said about the forbidden fruit of the knowledge of good as well as evil? Not necessarily, if the heart is not the same organ as discursive reason. "Why is the truth, it would seem, revealed to some and not to others? Is there a special organ for receiving revelation from God? Yes, though usually we close it and do not let it open up: God’s revelation is given to something called a loving heart” Fr.Seraphim Rose, God's Revelation to the Human Heart).
The case made by Nietzsche, that apart from God man stands in a situation "beyond good and evil" with respect to what can be grounded by autonomous man in philosophical ethics even forms an important part of the apologetic of Roman Catholic writer Hans Kung in his book Does God Exist? (a work written during the period when the Vatican still approved of him enough to bankroll a staff of scholars to aid him in researching his book) where he concluded that modern secular man is in an epistemic and existential situation where he must either choose God or nihilism (an argument not all moral philosophers or even theologians would accept, but Kung's arguably binary thinking aside the difficulty of scientific ethics remains as problematic -more so- than when Nietsche pressed it so forcefully). But rather than getting bogged down in the philosophical angle, what might theology suggest?
What we relate to (or do not) from a theological perspective -whether it is "subjectively apprehended" or not- is something Incarnational and Personal (or the lack thereof). Fr. Andrew Angiorus's brilliantly observes the presence or absence of love in our hearts is not at its root epistemological (though it may be *congruent* to epistemic themes) but psychological:
"'Therefore God gave them over in the sinful desires of their hearts' (Rom 1:24). Generally, atheists and agnostics are talking about themselves when they talk about the absence of God. They simply express their personal subjective truth (that their souls are empty) in an objective way and try to generalize their experience. In other words, there is no theology, or even philosophy here, it is just their own ill or deficient psychology, which is what atheism is... In the Scriptures Christ says clearly that only the pure in heart will see God. In other words, intellectuals, examiners and professors will never understand God, if their minds are not pure... How do we know if someone has a pure heart? The pure heart is evidenced by the way we live. As Peter says, a person devoted to the Lord “does not live the rest of his earthly life for evil human desires, but rather for the will of God” (1 Peter 4:2); "Who may ascend the hill of the LORD? Who may stand in his holy place? He who has clean hands and a pure heart, who does not lift up his soul to an idol or swear by what is false.He will receive blessing from the LORD and vindication from God his Savior" (Ps 24:3-5)." -Fr Andrew Anglorus
Yes there is a crisis of scientific philosophical ethics in the sense of the medieval and Enlightenment programs to ground ethics in discursive reason. But there is a living God who knows the thoughts and intentions of each heart and is nearer to all of us than our own skin, though our perception of this may be darkened by sin. It is because God is living and near that we are left without excuse.
John 12:35: "Walk while you have the light, before darkness overtakes you. The man who walks in the dark does not know where he is going."
Those who claim to be moral relativists or nihilists, if in their hearts they can accept that it is the same difference ethically (aside from personal consequence) to on the one hand teach a young babe what colors are, or that every star is a sun, or on the other hand to feed them to their dog rather than make the long trip for a bag of Purina, have become darkened, in a situation analogous to story of a public debate in Hyde Park (London) as told by William Lane Craig:
‘People tell me there is life after death; but I can’t see it! People tell me there is a heaven and hell; but I can’t see them!’ After he had finished, another man struggled to the soap box. He began, ‘People tell me that there is green grass all around us; but I can’t see it. People tell me there are trees nearby; but I can’t see them. People tell me there is a blue sky above; but I can’t see it. You see …I’m blind.” (William Lane Craig, The Son Rises, p. 19).