For tha sake of correctness, the thread will compare countries, regimes and movements which represented these ideologies. The argument that there was "no real" Socialist/Communist country might stand but they all aimed for it, and worked towards it. As for Fascism, the general broad view of Third Positionist governments will be taken, rather than Italian Fascism itself, this will though exclude right wing dictators who were not following any Third Positionist ideology.
The crimes of Fascist/Third Poistionist governments are no secret, and can easily be looked into given that they happened in a limited time frame, as well as mostly happening centered in Europe. As we all know, most of these crimes were committed by the National Socialist government and party of Germany, starting from their rise to power to their downfall. Aside starting a catastrophic war to feed it's ambition, it was it's brutal treatment and planned extermination of non-Germans, especially the Jews, which the world remembers. Fascist Italy, then the second largest combatant on the side of the axis in Europe, does not seem to have it's crimes well remembered. Having lead to the death of less people than it's German peer, it never the less committed horrible crimes in it's occupational zones, namely in Africa and the Adriatic coast, which range from war crimes to crimes against humanity, but also committed further crimes on their own soil, complying with Germany's anti-semitic policies. Other Fascist governments can be found in other axis alligned countries, such as Romania, the Independent State of Croatia, the First Slovak Republic, as well as collaborationist governments which held a Fascist conviction, such as Quisling's Norway or Nedic's Serbia.
This does not include Japan, which, even with it's similarities, never adopted a formal Fascist ideology, but rather an imperialist ultranationalist one. This can, admittedly be seen as a proto-fascist regime never the less, so we could include those victims too.
In conclusion: the contempt towards Fascist ideologies is widely known and a trait found in all modern democratic countries of the world, most notably those that fought against it. This contempt is mainly aimed at the National Socialists, and rightly so, given that they were the main "contirbutors" to such crimes against humanity.
But what about Socialist/Communist governments? In pure statistics, that death toll manages to "beat" the one inflicted by Fascism. The death caused by such regimes can be estimated to be ten times the ammount of the already mentioned Fascist ones. Unlike Facism, they happened through-out the globe, in a timeframe of nearly a century. It's long time existance outside of war, as well as it's application in different times and countries with different variations, is a good way to spot the failure of such an ideology as well.
While denial to horrible genocides such as the Holocaust is, thankfully, a crime in many countries, denial of Communist crimes, most notably the ones of the USSR, is almost not frowned upon, and sometimes there isn't enough light shed on it either. While anyone waving around a crooked cross are frowned upon, or the symbol might be even banned to begin with, waving around hammer and sicke signs is not as much frowned upon.
Which gives us the question: What causes such a thing?
I'd argue that it is pure ignorance. Many people try to point out how the USSR helped against Germany in WWII, but if one would look at the time before the war broke out between them, Stalin had no intent of attacking Hitler, in fact, providing him with valuable materials to fuel his war in the west. Not to forget that many countries which had suffered from Hitler's invasion fell pray to Stalin quickly after, experiencing five decades of torture and tyranny.
But also, it might have to do with the lack of education on that matter. Education has made National Socialist at least an unacceptable ideology in the modern world.
