I find your focus on totalitarian left peculiar. It's not like they were somehow unique - plenty of totalitarian regimes of all kinds have arrested and executed countless people for whatever.

A few random examples:

* Ottoman genocide of Armenians, on ethnic/religious grounds. The Ottoman Three Pashas regime was as far from left as possible, but plenty totalitarian.

* US internment of "foreign elements", including those with US citizenship, during both World Wars. US was never even center-left, let alone farther, and totalitarian is a stretch. Less bad than the other examples here, but still.

* The many White and Red terrors in the Interwar and post-WW2 years, where vague association was guilt and execution.

* Of course Jews, Roma, Gypsy, dissident in Nazi concentration camps.

* The Herero and Namaqua genocide by the rightist totalitarian-ish Imperial Germany.

* UK mass internment of Boers. Not leftist, not really totalitarian.

Need i go on? Why did you feel the need to pain totalitarian leftist as worse than any other totalitarians?