Of course some contemporary communists (not only Trotskyists) will emphasise the unique evil of Stalin as the true reason for the purges, censorship, totalitarianism, “class liquidations”, bureaucracy, racism, etc. of the Soviet communist system. In fact there are many retrospective Marxist theories about the failures of the Soviet and other communist regimes. All of which exonerate Marxism and communism from any culpability whatsoever. (E.g., theories about the Soviet Union being a “deformed workers state” and what have you.)
Can the systematic failures of all socialist/Marxists systems be blamed on Stalin and other despots? Clearly not.
Instead the problem is inherent in Marxism itself. At least that’s what Michel Foucault came to believe.
Foucault once wrote:
“In the Gulag one sees not the consequences of any unhappy mistake, but the effects of the ‘truest’ of theories in the political order.”
In other words, we're mistaken to look elsewhere for the failures of all Marxist or communist systems. It's not really about “the cult of the leader”, the “invading white armies”, “Western imperialist pressure”, “economic contingencies”, etc.: it's about Marxism itself.
So in light of the Gulag, the purges, Pol Pot and Year Zero, the Cultural Revolution, millions of dead, etc.: instead of looking at revolutionary Marxism as a never-realised ideal: we should look at the ideal itself. That's where the problem is. Indeed it's very odd to look elsewhere after all this time and all those communist/Marxist failures and mistakes. And that's precisely why only Marxists themselves have always looked elsewhere for the heart of the problem.
As a result of this, an open thinker will obviously reject the inherent harsh rigidities, diktats and totalitarianism of Marxism. So it will be no surprise to know that Foucault even went so outrageously far as to advice his students to open their minds (something a Marxist professor would never genuinely do) and read, of all things, the works of Frederick Hayek; whom contemporary Leftist automatons would regard as one of the granddaddies of today’s “neo-liberalism”. This alone would make contemporary Trotskyists and Communists reject Foucault (if not completely). Indeed he would certainly be classed as a “neo-liberal” for such academic openness. (Personal attacks and ad hominems can be found in nearly all Marx's own writing. Indeed it's full to the brim with viciousness and sarcasm: much of which is aimed at his fellow socialists and communists!)
Regardless of the tragic consequences of the free market, these economists and thinkers were libertarians – the exact opposite of communists and Trotskyists (from before Foucault’s day to our own). These people dared to make a blasphemous connection between the free market and individual liberty. They argued that economic freedom (though not only economic freedom) severely limited the power of the state. However, because all communists/International Socialists adore the state (their own state; not the ones they're fighting against) as much as any National Socialist (Nazi), they similarly hate libertarians as much as they hate what they call “Nazis” or “fascists” (i.e. everyone outside their tribe; unless a member of an ethnic minority).