If Stalin hadn't killed so many people, they would have starved to death instead. There simply wasn't enough stuff in the Soviet Union to feed everyone. His murderousness was, in context, a mercy. A relatively quick death.
If promiscuous mortality is already a given, why not be capricious and psychopathic? Why not just kill someone because you don't like his face? For every one who is saved, another dies untimely. And much slower. Unless they manage to have children before dying, then it's more than one.