The sort of people who might secretly incite and then stage a successful armed revolution and coup are probably expecting a coup, or at least a few revolutionaries in every party meeting. Not restricted to the left though.

Stalin got there by being a violent thug, he would stay there by being a violent thug. Ditto Franco in Spain, for at least a decade or so after the end of the civil war.

Repression of scientists, and minorities of all kinds? Difference of any kind from the party/dictator's view is to be mistrusted, thus purged, or at the very least repressed. See Saudi Arabia - which Franco's Spain resembled in its later years, with extreme repression of women and religious dogma.