Probably a  for that.
But it is a reminder that just as most people don't really grapple with the amount of good done since the agricultural revolution, they also can't grapple with the new types of evil that have been enabled since the dawn of the 20th century.
It is sunshine and roses this decade, but there are some much scarier threats in the future than, eg, climate change. WWII happened in a climate quite similar to our own.
There are a very large number of countries, an enormous range of political philosophies and "authoritarian" is a very broad brush that accepts a huge number of government styles (monarchies, churches, dictators, oligarchies, company structures, etc).
And we know that the liberal governments sometimes do horrible things too. America is responsible for vast numbers of deaths in, eg, the middle east.
Letting people be free is a better political ideology than authoritarianism; but claiming that authoritarianism = mass murder needs support. Every successful political ideology leads to some level of mass murder, there isn't a powerful country out there that hasn't initiated a war and suppressed internal dissidents violently at some point. It is a question of relative impact and scope. To support the claim there needs to be evidence.