Like allowing multiple political parties, full freedom of speech and assembly, abolishing the police, ownership of weapons, direct democracy etc.
The common justification is that they were in a dire situation where allowing too much freedom would allow counterrevolutionaries and foreign imperialists to sabotage and destroy them. I find this unconvincing, to what extent is security better than freedom? To what extent can the current leadership be trusted to "protect the revolution" than possible others better suited who couldnt take power?
Even then, why did the Soviet Union and other communist countries not democratize after WW2 when they arguably established sovereignty with their nuclear weapons?
Just as the capitalist ruling class preferred fascism to losing their power to communists, it seems the Marxist-Leninist rulers preferred capitalism to a more democratic form of socialism.
We see this happen now in Cuba, the last bastion of Marxism-Leninism, where the ruling class has been gradually introducing privatization and market reforms rather than allowing things like open elections, freedom of speech etc. Under capitalism, they can still rule.
I won't take credit for this since it isn't my original idea, but someone else on here pointed this out and it never clicked for me before then. American Liberals are quite fond of citing George Washington's criticisms of party politics as given in his Farewell Address.
They are very quick to pull this out of their back pocket when bemoaning the existential hostility and eternal deadlock which exists in Congress, but they never seem to realize that what Washington is essentially advocating for a one party state.
Now, I'm not the kind of nerd who looks up to George Washington as any sort of role model, but the dude is obviously respected throughout common society. I think it is good rhetorical move to pull this one out whenever you encounter Liberals dismissing political systems on the sole basis that they are one/no party states. This is a rhetorical tactic that Ho Chi Minh used famously at the outset of Vietnam's anti-colonial struggle. He quoted lines of the US Declaration of Independence verbatim to state on one hand "We're just doing the thing that you did. We're even justifying it in your own words," while on the other hand highlighting the hypocritical nature of a country which celebrates its revolutionary history while crushing revolutions all over the world.