Let's assume that all Ukrainians are Nazis.

Even in this farfetched scenario, nothing would justify the Russian aggression against Ukraine, nor those who justify it for this reason or any other (Satanism, Western hegemony, wish to join NATO, Russian “historical rights”, etc.).

Those who fought Germany in WWII, didn’t fight it because it was ruled by Nazis. Germany was fought and beaten because it waged aggressive conquest and extermination wars.

Without Nazism, a rightist, centrist or leftist Germany, even with a democratic government system, could have had the same expansionist and hegemonic aims, and could have waged a cruel and destructive war as Nazi Germany did.

Germany was not destroyed because it was a Nazi country, but because it had to be stopped from destroying other countries. This would even be true if the rulers of Germany had been Christian Democrats or Social Democrats.

For example, the USSR didn’t fight the Germans because they were Nazis. From 1939 to 1941 the USSR was a loyal and useful ally of Nazi Germany. The USSR fought a defensive war against a German invasion that occupied, destroyed, and looted most of its European territory (Baltic States, Belarus, eastern Poland and Ukraine) and the Soviets fought it because they had no other choice. 

Those judged in Nuremberg and in the following trials, weren’t judged because they were Nazis. They were judged for crimes they committed while they were Nazis. Not for the “crime” of being Nazis.

Nazis, be they Russian, Ukrainian, British, French, German, Spanish, American, etc. —as despicable we may find them, are human beings and have human rights. If they violate the laws, the legal systems exist to judge and punish them.