You would have traded everything you own and then the Nazis would have killed all the Jews anyway. They were planning to do the same with the Slavic populations of Eastern Europe too after they beat Russia, by the way.
The death toll would have been much higher had we let Hitler do want he wants. Putin is not in thew same league but the same principle applies.
But if we're talking purely about the Holocaust, as soon as I take up arms I make myself more of a target. Better to go in unarmed and try to help them escape. Part of the problem was, at the time it cost £5,000 per person for a Jew to emigrate to Palestine, as set by the British. Many more could have escaped if that hadn't been the case.
I don't think I am against taking up arms, when it comes to something like ISIS. The mission there was to destroy their equipment (which we gave them). Should Britain have declared war on Germany when Hitler invaded Poland? Should the US have stayed out of the war? I'm not sure if Hitler originally intended to invade Britain, but it has been suggested that far less people would have died if the US had not got involved. I gather that the appeasement arrangement was to do with allowing Germany to occupy German-speaking lands such as Austria.
If as you say Putin isn't in the same league as Hitler, maybe it would be wiser to wait until he crossed the NATO line before getting involved militarily.
Of course it's linked although the war is not the only thing contributing to the crisis. What are we supposed to do about it though? Are we supposed to hang Ukraine out to dry? Are we supposed to give in to Russia? In the long term, the latter could be very costly indeed.
I've found an interview with someone in the DPR's army concerning the role of Russia in Donbas. He reminds us that the war started in 2014 with the coup d'etat. After the peace agreement of 2015, the separatists reduced their army to 10,000 which they kept in order to hold back the AFU. It became clear that Ukraine wasn't going to keep their side of the deal, which was for autonomy of Donbas within Ukraine, and that they would try to take Donbas back. That is why they asked Russia for help - because at that point they couldn't build their army up to strength in time to stop the Ukrainian army invading.
Given this, I don't think 'we' should be involved at present.