I find this liberal doggedness in the belief that Alger Hiss was treated unfairly to be rooted in one of two reasons:
Either they know the truth but still refuse to see it, or they accept it, but think he was advancing the cause of communism, which is their religion.
Neither of those is a good thing.
The Left has a difficult time with facts, though I noted that some prominent Leftists were aware they had been wrong during the early years of the Cold War, hypocritically not altering their latter day views (that had been based on their faulty assumptions about Russia and the Cold War).