I think the implication here is, "would you rather be in the Great Purge or the Holocaust", and people seriously overestimate how big the Great Purge was. Not that it didn't suck for anyone who got drawn into it, but let's have some perspective: it lasted about a year and a half and at its worst there were still fewer Soviets being imprisoned than there are Americans being imprisoned today. The purge stands out because the baseline of Soviet repression was so much lower than it was during that period, while the modern prison industrial complex is something we've gotten used to for generations.
The other thing they might be getting at is the famine of 1930-33 - but that also killed fewer people than the Holocaust, far fewer people when you take into account total population. Of course, the famine killed everyone more or less equally, while the Holocaust targeted groups the Nazis didn't like - so perhaps the average redditor is making a calculated decision about which regime they would be more likely to survive after all.