Heed the warning? Within a couple of years Stalin had began an extermination program that made this look like a picnic, and nobody cared. Mao managed to outdo Stalin and look how much business we do with China. Meanwhile the Soviets will be hosting the next Olympics. The only reason we hear about Germany is because they lost. Society hasn't learned a thing except how to conveniently forget.
The difference is that the Nazis had the audacity to actually film their atrocities, they took so much pride in it, they wanted to chronicle it for their own posterity.
Don’t forget the Abortion clinics in the USA. over 40 million unborn killed for the cause of the left and the demonkrats.