That's a pretty small sample of examples, and they all pretty much could be considered to relate to the same set of beliefs, communism.
So maybe communist ideologies have been used for as bad crimes as religion. But that doesn't prove for all lack of religion. In fact there's another example that proves a great many good to the lack of religion, that of democratic ideologies.
Now if I hypothesize, it seems I see a pattern, any time power is given absolutly to a fixed, non changing group of leaders, whose only mean of overthrowing is through force, it seems to cause atrocious violence. Such as when religion governs, or single ideologies such as communism or fascism governs, or when a single person in the form of a dictator does. Hence why democracy does slightly better.
On that note, ideologies that have as a goal to reign absolutly and supremely, which almost all religion have, and some other non religious ones, like communism and fascism have, then you can probably predict a long term negative impact of society, overshadowing all short terms benefits the ideologies might at first demonstrate.
It's also possible to attribute the harshness of communism to having to overthrow another entrenched great power, that of religion. So it should be considered, would a democratic state transition without atrocities to a communist one? Probably. Similarly, a democratic one would probably transition without atrocities to a religious one also. And this all goes back to having a way to transition that is alternate then simply through force. Any transition from a religious state, or a absolute ideology state, like communism, will require atrocious acts, because such state have no other means of self-adapting or correcting themselves. They're not agile in any way.