Political heresy is more of a threat to the collective than is a thief or murderer. The common criminal only affects a few people. A heretic can affect all of society.
This insight is almost directly from Aleksandr I. Solzhenitsyn’s book The Gulag Archipelago, Volume 2: An Experiment in Literary Investigation, 1918-1956. This is why the political prisoners were treated worse and had longer sentences than thieves and murderers.
It also might explain why the political left in this country are so violent toward their political opponents. They, at some level, have reached the same conclusion as their political brethren of the former USSR. And that is that independent thought is a threat to the entire power structure and the very foundation of their existence.