No fun, either.
>Nazis wanted to help others not being eslaved by International Jewry
Except that they wanted more than that. Like to kill all Slavs, Romani, disabled people; get revenge on France despite the war being more Germany's fault than France's anyway; invaded sovereign countries that were not a threat to it like Denmark and Czechoslovakia; etc., etc. From any D&D standpoint the Nazis are clearly evil regardless of what you think of the Jews.
>Communists wanted to help others get rid of old oppressive world by killing everyone
>by killing everyone
Operative word there.
>What good (lol puns) does a system that puts them all on the same side is?
They're not all on the same side, though, and it's morally childish to assume that they are.
>What actions are justifiable and under which conditions.
I don't have to, Wizards of the Coast already did: en.wikipedia.org/wiki/Book_of_Exalted_Deeds
Literally the first twenty or so pages are devoted to defining what "good" means in D&D. Except for "casting good spells", for obvious reasons, none of it seems nonsensical when applied to the real world.
> you will run into a BRICKWALL of special cases, complex perspectives, arguments to be made.
There is never a brick wall, there is only an incomplete understanding, or deliberate misunderstanding, of the situation, i.e., user up there trying to say "the Nazis just wanted to help people, so obviously it's Good to help the Nazis".
>Real world sensibilities
That's just the phrase we use when we don't want to say "I want to do the right thing, but it's too hard/too expensive/I just don't feel like it."
But that's what we're really saying.