Never underestimate the value of a good bad example.
Well-deserved praise has been heaped on those who answered the call of duty to defeat militarily the Axis powers in World War II. If you ignore the fact that we couldn't have done it without our own ally, that sweetheart Joseph Stalin, it really was a clash between Good and Evil.
The Nazis in particular did future generations a favor by being so categorically and undeniably evil. Of course they didn't view it as evil. They considered it an admirable rigidity of principle, and the iron will to carry out a ruthless plan to impose a virtuous monoculture across the globe. The urge itself is evil, but it has its adherents even now.
Because World War II came along when humans had developed film, broadcast, and recording technology, and because the Nazis were so stuck on themselves that they kept meticulous records, we have a lot of detailed history about who did what when. We can rapidly draw parallels to current events and show without a doubt what can happen when the logic of a hateful ideology is drawn out to its grimmest conclusion.
Mass killing is a human tradition. Some instinct impels us to try to wipe out rival DNA, to compete for global domination, starting right in our own back yards. It doesn't happen everywhere, all the time, but it recurs enough throughout history to show that we have a chronic problem. Returning to the bloodbaths of the mid 20th Century, we find plenty of historical records related to every theater of war and land under occupation. Other examples than the aggressive Nazi regime haven't had the great marketing that makes the Third Reich such a strong brand, but the idea of killing people who don't agree with you needs no introduction, wherever it arrives.
It is this very archive of evil that gives us the graphic rebuttal to plans put forward now in countries that once considered themselves bastions of freedom. The hypocrisy of the United States is unfortunately evident in the persistence of official and unofficial racial segregation after the Second World War, but at least some efforts were made to acknowledge the rights of more than just white guys as the 20th Century passed the half. Those very efforts solidified the core of evil that predated the Nazis by a couple of centuries in our great country, and that sympathized with the actual Nazis in their rise to power.
Recognizing an evil does not automatically cure it, but it is the vital first step. Parallels to the Nazis are too freely drawn, but the sensitivity to Nazi-like encroachments is an early warning system for the advancement of a truly free and inclusive society.
The monoculturists consider the desire for a free and inclusive society to be the evil. They despise the weakness of accommodation. They pride themselves on their admirable rigidity of principle and iron will. That's why we keep having this argument. They must be refuted on principle, not just bested on the field of combat. In fact, combat merely obscures the real issues in a cloud of smoke and a spray of blood. That's why hardasses would rather fight a war than lose an argument. War is exciting, and some day they might win. Until then, they'll take whatever beating they have to, and retire, grumbling, if it goes against them again.
The real Greatest Generation will be the one that confronts and vanquishes its own evil in quiet meditation, and never inflicts its misery on the rest of the world. While I would welcome that at any time, I'm not holding my breath. Every generation has to interpret the world they find, and choose a way through it.