When one looks at the history of Marxist-Leninism, what they have to look back on are dictatorships and purges. While there are obviously revisionist attempts to make the USSR look better than it actually was, that is usually post-conversion rationalizing rather than something any unbiased observer would believe.

Meanwhile, there is a relatively libertarian strain of communism supported by various Left Communists that seems far more appealing to just about anybody who likes Marxism but likes having their freedoms protected too.

Why then does Marxist-Leninism persist? Certainly the theory can't be that appealing, in practice it is horrifying, so what keeps it alive?