They don’t know history
The Trotskyites were killed first
Even more important is the realization that factions like the Trotskyites MUST be killed.
If Trotsky’s faction had held sway, it would have been the followers of Leninism who would have been eradicated.
You can’t have a dictatorship when there are multiple voices. There can be only one voice issuing the diktats.
And Leftism in all its forms is dictatorship.