FROM THE COMMENTS BY 'GFC':
I believe the Left to be the child of Satan, and in this we see that the rotten apple doesn't fall far from the diabolic tree: the devil cannot create of his own accord but can only twist what has already been created into corrupted forms. Always the devil tries to ape the creation of God.
The modern Western Left works its part in this by undermining and eating away at legitimate authority, but once that work is complete, attempts to set itself up in the only way it can: as a funhouse mirror image of what it worked so hard to destroy.
This is why the Left today doesn't try to destroy institutions like the Church outright but rather corrupt and subvert them. They don't wish to do away with authority per se, only usurp those rightfully in authority and rule in their place.
As in many other respects, the modern Left (political correctness) more resembles the late, cynical and corrupt Soviet Union (Brezhnev era) than it does early and idealistic post-revolutionary Communism.
The Old Left tried to destroy whole institutions such as the cultured aristocracy, scholarly private schools and universities, independent scholarship, the serious Christian Churches.
Early Soviet Communists did this to the Orthodox Church+ (which still had immense status and power even in 1917) initially mostly by violence: imprisoning, torturing and killing vast numbers of bishops, monks and priests, and devouts adherents - by invasions, confiscating resources, wholesale demolition etc. (See also Solzhenitsyn's massive documentation.)
The New Left attacks on institutions are legal, regulatory and legislative; harassment is by official investigation and taxation, key individuals are publicly vilified by spreading lies and libels, the mass media is used for mockery and humiliation, employment is undermined, official scapegoat status is conferred, police protections are removed - and so on.
Unless, of course, these institutions tacitly acquiesce in their own re-making and re-direction - in which case they are showered with money, privileges, honours, and official admiration.
The New Left, as you shrewdly point-out - aim to preserve the hollowed-out shell of these institutions - and to fill these shells with inverted content (e.g. the aristocracy replaced by titled subvertionists, educational institutions by social engineering certificate-allocators, independent scholarship by state-funded 'research' bureaucracies++, Christian churches by this-worldly hedonism-sanctifiers and propagandists for 'the welfare state' etc.).
Again, the late Soviet Union were pioneers in New Left tactics with respect to the Orthodox Church.
After an decade or so spent in an orgy of blood lust, the State instead corrupted and subverted the Orthodox Church into a branch of the state bureaucracy by hollowing it out and inserting Communist personnel, functions and ideals; atheist KGB officials were put into in Bishop's jobs, Churches were used to spread Communist propaganda and engage in spying and surveillance.
A shell of surface continuity was maintained - while the official 'Orthodox Church' was enlisted to promote national cohesion and nationalistic zeal.
The West is nowadays full of 'official' Orthodox Churches.
Indeed, there is very little else...
++ It is insufficiently acknowledged that the Royal Society of London - once the premier scholarly institution in the world, descended from the actual originators of modern science - is now merely a branch of the UK public administration; receiving the great bulk of their annual funding from the state in return for providing useful pseudo-scientific validation of government policies:- such as their support for the new quasi-religious moral dogma of 'Anthropogenic Global Warming' due to carbon dioxide pollution.