Many Christians have for many centuries wanted to be able to argue that evil was an insane unjustifiable irrationality. That it made no sense. That the only thing which did make sense was to live in obedience, and conform to the single reality that is God's creation - in the strongest possible sense that there is nothing else but God's creation. So, to be evil is to reject the only reality.
One important half-truth behind the "relativistic" ideology of the dominant West-Globalist secular Leftism, relates to its rejection of this traditional "objective" Western Christian conceptualization of good and evil as reality versus anti-reality.
For traditional Christianity - as (I understand) for Judaism and Islam - Good was theologically conceptualized as bound-up with God as the sole source of creation (God created everything from nothing); therefore Evil was conceptualized as objectively irrational, because it is against everything.
Good was therefore conceptualized primarily in terms of conformity to God.
With this scheme, there was no positive role for Man's freedom and agency except to submit to the divine order; because there is nothing except the divine order.
There is only one coherent choice for each Man, for each Beings, in such a scheme - which is to choose allegiance to God - thus all evil is necessarily incoherent and insane*.
Against this the false-half-truth ideology of secular Leftism proposes some version of "relativism", of the non-objectivity of values -- which is calibrated against the bottom line "hedonic" assumption that mortal life is the only life, and that the values of mortal life are therefore (merely) means towards the end of maximizing happiness and/or minimizing suffering.
In other words, by this account, truth is whatever happens to make me most happy (or those I care about) over some timescale that I prefer - whether immediate happiness, or some kind of predictive happiness ranged over some future span.
The more recent conceptualization that swaps happiness for the double negative-freedom-from-suffering , works the same way. Truth is just expediency with respect to minimizing suffering on a timescale from now, to some variably longer span.
But relativism is itself incoherent for many reasons, as has been known since antiquity. It has no basis for asserting its own validity.
And, after all, why is it assumed to be better to experience happiness and avoid suffering? Supposing I, or somebody else, says the opposite - then that is as true or untrue; and the choice between inverses depends on some utilitarian prediction of the consequences. In practice it is facile to argue that suffering now leads to happiness later - or the opposite; and the wrangling never stops unless coercively imposed!
If there are no objective values and all opinions are equally valid; then this assumption, and all other values, can be inverted - for any reason, or for no reason.
Yet relativism - in a soft and short-termist sense - clearly has some kind of powerful and lasting appeal when measured (as it is) against the "traditional Christian" version of values as objective, impersonal, and therefore a matter of submissive obedience to what is asserted to be the nature of reality.
I think the element of truth in relativism is embedded in an individual intuition that a moral system which utterly downgrades "my" individual conscious human to (near-) irrelevance, cannot be right.
When morality is made utterly objective, nothing to do with me - it becomes simple tyranny.
Surely real, spiritually-compelling, mortality must be something that is in each of us, from each of us - and not just a thing "out there"?
Surely we must be able to choose our values, or else they aren't values?
And surely our choice depends on what each of us is by nature and wants most; on what each of us regards as good - and surely this is the primary moral act?
We are confronted by reality - and (on the basis of our specific personal nature) we must and shall choose what will be our overall attitude to that reality?
From this perspective, good does not feel like a wholly external reality, and evil does not feel irrational or incoherent; but both and either a choice rooted in what we personally most want among various possibilities.
Then; whether we want it here-and-now, or want it in the long-term (a long-term that potentially might extend to eternity).
So - In mainstream culture, we are apparently confronted with two incoherent and therefore false alternatives: the "Christian" supposedly being an objective and impersonal morality in which individual discernment has no positive function.
Or there is a nihilistic fatalism where there are no values, but only an unbounded choices between arbitrary individual preferences - presumably based on the fluctuations of current feelings and emotions. In practice, the choice between-relativistic moralities seems to hinge on relative differences in the power to coerce and deceive, desire to belong to particular groups, and the like.
My conclusion is that both alternatives should be rejected because incoherent hence false; and the truth needs to be sought in some other scheme of things.
The truth embedded in relativism is that it is possible, rational and coherent that some people (and other beings) can and would choose to reject God and divine creation; would choose Not to affiliate to God's hopes and plans.
And that rejection is the essence of evil.
This rejection is a choice rooted in the fact that although we all are created Beings, are indeed Children of God; we are not entirely so - and we each and all "contain" aspects of that primordial self from-which we were created - and these primordial selves are each unique.
Some primordial selves are less able (or perhaps unable) to love, or maybe the love is present but very weak and a low priority compared with other desires.
Therefore, when confronted by God's creation which is rooted in love and aims at a reality of love; there are some beings who reject that vision - and who are therefore evil.
(So, I am defining good and evil by either affiliation to God's creative will and plans - rooted in love - or else the active rejection of that, for any reason.
(There is also, I believe, a theoretical possibility of a wholly passive and personal declining to join the work of creation - a simple opting-out; without any attack on creation or any attempt to persuade others to reject God. Just a cosmic "no thanks" and a reversion to unconscious unawareness in isolation. If this happened, we would not know anything about it except that a being would "disappear" from creation.)
As I said, some Christians (and others) want to be able to state that this rejection is incoherent, irrational, illogical - and that evil is objectively-impersonally wrong.
They want to say that evil is: Just wrong without reference to any consciousness of any Being.
But I would say that the objectivity of the wrongness of evil derives from the fact that by rejecting actual divine creation rooted in love, an evil Being ultimately places itself against creation as such.
To be against creation is not relativistic; it is an objective fact about a Being's relationship with God and divine creation.
Thus values are not subjective, nor are they objective - values are about a relationship.
Evil is not a "mistake" of itself; but is a choice. There may be a mistake in terms of an evil Being wrongly predicting the consequences of rejecting God, rejecting love, rejecting creation...
But the error is not a logical one. Its more a matter of getting what you asked for, but not liking it when you've got it.
*(Why it is possible for Men, or anything, to reject the divine order? If the theology says that such a choice is incomprehensibly insane, then where could this desire comes from in the first place except from God Himself? This logical incoherence has never been clearly explained; and indeed it cannot be made coherent. Because because if God created absolutely everything that exists, then the desire to resist God must ultimately have been created by God Himself - as must all evil. Saying that God gave men Free Will does not answer this - because agency can only operate using the materials provided by God, which must mean that God made the evil in the first place, for evil to be choose-able. Yet for Christians, specifically, God is known and said to be wholly Good - so how (for a Christian) could a wholly good God provide evil for free will to be choose-able? My answer (in brief) is that God is wholly Good, and did not make evil - because God did Not make everything from nothing; but instead created using pre-existent Beings; some/most/ all of whom were capable of evil by their primordial nature. Thus evil has always been present in reality - and God is creatively working towards Goodness.)