People get confused about the nature, and even the existence, of evil - but if one recognises the reality of Good, then evil is straightforward: evil is the strategic destruction of Good.
(Good may itself be operationally-defined as Truth, Beauty and Virtue in Unity - TBV in U - with TB&V being regarded as real and objective values.)
Strategic means purposive, deliberate; that evil works over time with the objective of destroying Good.
(Note: It is not necessary that evil is self-aware that it is aiming to destroy Good - indeed most evil is done by the self-deceived; dupes and servants of only a small - but necessary - minority who know what is Good and know that they are aiming to destroy it.)
But destruction of good can be done in different ways, and at different extremes. So actual destruction of the Good is a middle term in a spectrum. That spectrum is Subversion, Destruction and Inversion - or SDI.
Think of marriage, as an example of Virtue - a Good institution. Evil first works by subversion of marriage - for example by propaganda (including works of art - novels, dramas, movies...) focused on the miseries and injustices of bad marriages, constraints of marriage, the joys and excitements of un-married and extra-marital relationships etc.; and by laws for 'no fault', quick, sanction-free divorce to encourage the breakdown of marriages. Marriage is weakened by subversion, to the point that strong marriage becomes statsitically rare and the 'normal' or average marriage is seen as a feeble, evanescent, faddish kind of thing.
At a greater extremity; evil may try to destroy the institution of marriage, to eliminate it altogether. This could be done incrementally, by making it acceptable, then fashionable, then positively valued to cohabit without marriage - and removing any social differences between cohabitation and marriage. It could be done by discouraging marriage through taxation, and unjust arbitration - favouring spouses who are the most selfish and short-termist etc. At the ultimate, marriage could be abolished.
Inversion, however, is actually a greater extremity of evil than destruction. This is important to understand - because it is a fundamental insight into the nature and motivation of evil without which it may be difficult to detect and to resist. The greatest extremity of evil is to invert the meaning while having people assume that nothing important has been changed.
So, beyond the evil of destroying marriage is the greater evil of inverting the nature, content, meaning and purpose of marriage, while maintaining that what results is real marriage. Inversion of marriage is a greater triumph and provides a greater satisfaction to evil than would the deletion of marriage from human society.
Or consider the virtue of Beauty as a different type of Good, from the perspective of SDI. Evil might subvert beauty - for example by inducing people to judge the quality of art in accordance with the sex, class or race of its producer, or the nature of the society which produced the work. Or beautiful art may be attacked and destroyed, or looted - as has happened in various times and places under the excuse of religious iconoclasm. But at the extreme is inversion of Beauty - especially ugliness praised for its beauty: examples include praise, prestige and professional prizes given to objectively-ugly art, architecture, novels, music and poetry (this is, of course, standard mainstream practise).
If Truth is the focus, as in science, the Inversion has been almost-completed. The social structure of science (funding, personnel, buildings, machines...) has been vastly expanded; but inside this structure the value of Truth has been removed and replaced. Science is now almost-wholly a generic managerial bureaucracy. The Truth has been hollowed-out and replaced by values such as career, public relations, money, and political values. Science has been inverted, yet people have not noticed - and still praise and support science as if it had something to do with the Truth.
My main point here is that inversion of Good is a greater evil than destruction of Good.
To have the Good denigrated as evil, to have evil persons and institutions lauded as exemplars of Good - such is the ultimate triumph of evil; and such is quite normal and usual in modern society.
The reason why inversion is a greater evil than destruction is that the war between Good and evil takes place in the spiritual realm; and the ultimate aim of evil is to create a situation where people - that is human souls, the true inner self - actively choose to reject the Good because it is Good, and instead actively to choose evil as their personal Good.
And for this purpose, inversion is far more effective than destruction.
The fact is insufficiently appreciated, hence the suggestion of an SDI abbreviation for the spectrum of evil from Subversion to Destruction to Inversion, as a way of remembering it.
Note: Probably the greatest and most crucial victim of SDI has been sexual identity - sexuality itself: man and woman as the differentiated, complementary, binary-basis of the eternal divine human soul. As an exercise, I leave the reader to work-out just how sex has been subverted, destroyed and inverted for apparently a majority of the Western peoples. This must surely count as the most remarkable and improbable - therefore deadly - triumph of evil over fundamental values thus far in recorded history.