We need to learn from history. Appeasement emboldens fascists. Russia in Ukraine is like Germany in the Sudetenland.
There is a lot to learn from history beyond WWII. For example, one thing we can learn from is the history of the exact analogy you're using being employed to justify wars. High ranking officials used that analogy to justify the Korean War, the Vietnam War, and the War on Terror. Looking back, the analogy doesn't hold up at all in any of those cases. But in each case, the propaganda push at the beggining of the war convinced large majorities of Americans to support it when it started. I don't think there's been a war since WWII that the US has been involved in where someone wasn't invoking that analogy. Quotes
Another thing to learn from history is the direct context of the war. The conflict began between Ukraine and the separatists in 2014, and a cease-fire was signed to stop the bloodshed. Ukraine violated that cease-fire, and that's what prompted Russian intervention.
The third point I want to make is that there's another lesson that can be drawn from the abandonment of Czechoslovakia to the Nazis. Unlike Ukraine, the Czechs were actually in a military alliance with the Allies. They did not just stand by while a neutral country was invaded, but broke an agreement to throw them to the wolves. And the Czechs had no recourse to hold them accountable, because when you're the dominant hegemon, rules don't apply to you. And yet somehow, this is constantly being used as an example of why we should trust our leaders, in the same powerful and unaccountable position, to have the best interests of the people of other countries at heart?
I find that absurd. The lesson I take from that is that people in those positions can sacrifice huge numbers of people, entire countries, to horrible fates, just to serve their own interests. And feuling the conflict in Ukraine, while refusing to consider any peace negotiations, is doing exactly that. They'll feed Ukrainians into the meat grinder the same way they'll abandon Czechs to the Nazis, and the same way they brought death and destruction to the people of Korea, Vietnam, Afghanistan, Iraq, and many more.
Oh, and one last lesson from history:
…That policy which pretends to aspire to peace but unerringly generates war, the policy of continual preparation for war, the policy of meddlesome interventionism. There was no corner of the known world where some interest was not alleged to be in danger or under actual attack. If the interests were not Roman, they were those of Rome’s allies; and if Rome had no allies, then allies would be invented. When it was utterly impossible to contrive such an interest — why, then it was the national honor that had been insulted. The fight was always invested with an aura of legality. Rome was always being attacked by evil-minded neighbors, always fighting for a breathing space. The whole world was pervaded by a host of enemies, and it was manifestly Rome’s duty to guard against their indubitably aggressive designs (Joseph Schumpeter, writing in 1919)
Does that remind you of anything? Because it sounds a lot like US foreign policy to me.