I think the core of the problem lies in a particular mindset that is not unique to either end of the political spectrum and in fact has existed in one way or another as long as there's been a western civilization to speak of.
It is best described as a "revolutionary eschatology" wherein all of society is - knowingly or not - locked in an all or nothing death grapple of good against evil, and all of history is a testament to this struggle. Religious fundamentalism is, perhaps, the most quintessential example of this sort of mindset. Preoccupations with the imminent rise of the antichrist and the need to prepare by means of reasserting religious and cultural purity so as to avoid or forestall the coming tribulations have been seen in countless forms not just in this age of a new millennium and among the sundry revivals of religious fervor seen recently in both in the US and in the middle east, but throughout a very long history. In his 1957 classic 𝘗𝘶𝘳𝘴𝘶𝘪𝘵 𝘰𝘧 𝘵𝘩𝘦 𝘔𝘪𝘭𝘦𝘯𝘯𝘪𝘶𝘮, British historian Norman Cohn demonstrates that this kind of thinking goes back literally to old testament times. His description of the underlying mindset is nothing short of poetic:
"The world is dominated by an evil, tyrannous power of boundless destructiveness. A power moreover that is imagined not simply as human, but demonic. The tyranny of that power will become more and more outrageous, the sufferings of its victims more and more intolerable - until suddenly the hour will strike when the Saints of God are able to rise up and overthrow it. Then the Saints themselves, the chosen, holy people who hitherto have groaned under the oppressor's heel, shall in their turn inherit dominion over the whole of the Earth. This will be the culmination of history; the Kingdom of the Saints will not only surpass in glory all previous kingdoms, it will have no successors."
Secular variations of this mindset also exist. Marxism prophesied a coming armageddon between proletariat and bourgeoisie. Hitler was adamant that it was "now or never" as far as the Aryan race vs the Jews was concerned. Approaching the new millennium, the religious right at home and resurgent Islamic fundamentalism in the middle east peddled similar themes. But these were never just strictly religious movements, they also appealed to real world grievances - just or otherwise - of common people in their respective societies.
Today, the beat goes on. The alt-right is sounding the alarm that western civilization will not survive unless third world - especially Islamic - immigration is halted and the pernicious influence of "cultural Marxism" in the media and in academia is neutralized. Sinister Jews may or may not be at the heart of a conspiracy to destroy western Christendom which can be, but not necessarily always is, reimagined as the white race.
None of this is at all new. Alt-Right type groups have been around as long as the Declaration of Independence itself. Specifics may vary, but the common themes of imminent decline and sinister conspiracies persist. Be they anti-Illuminati and anti-Masonic conspiracies of the 18th and 19th centuries, or McCarthyite, John Birch Society red scare stuff more recently, there's little new about any of it. The only things I'd see on 4chan or The Right Stuff today that I would have not seen in the American Mercury circa 1960 (or today, for that matter) are Pepe the Frog and Moon Man.
There, as always, is a diabolical conspiracy best described by Richard Hofstadter in his 1963 essay, The Paranoid Style in American Politics:
"The central image is that of a vast and sinister conspiracy, a gigantic and yet subtle machinery of influence set in motion to undermine and destroy a way of life. One may object that there are conspiratorial acts in history. and there is nothing paranoid about taking note of them. This is true. All political behavior requires strategy, many strategic acts depend for their effect upon a period of secrecy, and anything that is secret may be described, often with but little exaggeration, as conspiratorial. The distinguishing thing about the paranoid style is not that its exponents see conspiracies or plots here and there in history, but that they regard a "vast" or "gigantic" conspiracy as the motive force in historical events. History is a conspiracy, set in motion by demonic forces of almost transcendent power, and what is felt to be needed to defeat it is not the usual methods of political give and-take, but an all-out crusade."
These are the terms in which "cultural Marxism", or should I say (((cultural Marxism))) are expressed. But it is not unique to the far right.
Those who tend to be tarred with this cultural Marxist label, known to us on the alt-left as the regressive left, peddle their own version of the same kind of narrative. Donald Trump is their version of the antichrist - the embodiment of white male privilege, arisen to lead his basket of white cishet male deplorables and visit tribulations and persecutions upon women, LGBTQ people and people of color: the postmodern equivalent of God's chosen people in the eyes of the SJWs.
Nothing new here either. The far left has its own long history dating back to the French Revolution in Europe, and utopian communities in America. Marxism is the best known but by no means the only example. Running the gamut from late 19th and early 20th century socialist and anarchist movements, to the pro Soviet Communist Party, to the New Left of the 1960s, radical environmentalists and through to today's SJWs, a similar secular manichaeism exists.
The common thread running through all of them is just how alike their paranoid right wing and religious millennialist counterparts they all are. America is seen as a vast, oppressive monolith hell bent on enslaving or destroying the proletariat, the 3rd world, women, minorities, immigrants, native Americans, LGBTQ people, the poor and so on, who also tend to be seen as a kind of chosen people, destined to show the way out of a destructive, unsustainable and oppressive consumer-capitalist society and into a kind of postmodern new Jerusalem. A restoration of the garden of Eden, often reimagined in socialist, matriarchal or non-European terms.
Given its longevity, it's likely that this regressive style is likely to remain a fixture in some form or another for the foreseeable, and perhaps the indefinite future. They cannot, it would seem, be defeated entirely, for if one form is suppressed another has been seen to rise and take its place. But the pattern can be recognized. Enlightened policy aimed at mitigating the social factors that give rise to the regressive style, thereby keeping its influence minimal, is likely the best we can hope for.