I think everyone does think of Russians as victims in WWII. Their own government signing Molotov–Ribbentrop to start with probably contributed to that, though.
Why, despite this history, are their concerns about Nazism in Ukraine not taken seriously?
Because there is no evidence that there is significant neo-nazi activity in Ukraine and certainly not amongst the government.
Also the Israelis haven't done anything this blatantly unprovoked in recent history, the Six Day War was over 50 years ago and even then there's evidence it was preemptive. And there was widespread support for the Nazis in the Arab world with Arab governments continuing to have economic and diplomatic ties with them throughout the war, so even that point doesn't hold water.
