Not all brutality is made the same. For Nazi Germany it was because Germans were "superior race" and others the scum of the earth, including Jews and such who were seen as subhuman. Death and destruction was part of their agenda starting from the Main Kampf.
For USSR, the persecutions were the result of defensive paranoia and over-reaching (e.g. in the early days) and power plays, but those that were sent to the Gulags or executed were merely seen as traitors, as often happens in revolutions (e.g. 300.000 people executed in the French one) and civil wars.
Sure, most of it were ploys from the party elite to keep their power, but that doesn't mean the regular people didn't share a dream of changing the world for the better. In fact so much so, that they inspired people all around the world.
Heck, European colonial powers resulted in the deaths hundreds of millions (from Latin American natives, to Aboriginals and to all the proxy wars and land grabs they participated in thousands of miles from their borders were they had no place to be) and enslaved 2/3 of the world (including ALL black Americans before the 20th century), and they are painted as A-OK (because they won and they got to write the history from their perspective). And that was pure greed and cynicism -- not some over-encompassing vision for some free humanity.