The plausibility of the Vs in the original miniseries is certainly in question. But its best parts are, as Christopher said, the elements of allegory. Along with the "rise of Nazism" portion of the story, there was the explicit homage "To the heroism of the Resistance Fighters — past, present, and future." It wasn't just the hows and whys of a people allowing themselves to become oppressed, but it was the fundamental TRUTH
in resisting oppression, regardless of how it presented itself. So while parts of the premise may have been questionable, the story itself was so good that the motivations of the Vs weren't as important as how their efforts spoke to some fundamental human truths.
Sadly, the Final Battle and Weekly Series all but abandoned those truths in favor of action and plot (which made the fundamental plausibility become much more prominent factor).