<National socialism is considered right-wing because it's nationalist, whereas extreme left socialism, aka communism, is international in its scope. That's the difference.

Doesn't hold a lot of water. I don't see a lot of difference between the German Fatherland and the Soviet Motherland, except that the Soviets managed to kill a lot more of their own citizens, even if not in such a cold-blooded clinical way as the Nazis. I would bet that the Third Reich, had it won the war, would have wound up just as "international" as the communist revolution. The key here is collectivism vs. individualism, and centralized totalitarian power vs. freedom, and these criteria should be used to judge political systems.

National Socialism is the opposite of communism only in the minds of communists, and for obvious political reasons. The reason Peron and other dictators are painted by the communists as their political "opposite" is because he was the enemy, not because his political methods and ideals differed in any marked way from their own.

"Leftist" thugs and "rightist" thugs are not opposing views, they are two nearly identical entities fighting over the same turf. Not cops vs. criminals, but simply two different criminal gangs in opposition. Think "Crips" and "Bloods."

Most normal people, including I would venture to say most of us on this board, correctly see "right wing" dictatorships and "communist" dictatorships as two sides of the same coin.

"The opposite of the extreme is the center." It's a lot easier if you visualize the political spectrum in more than two dimensions:

Okay, getting back to the interesting part (the books):

"It Can't Happen Here" was written by Sinclair Lewis in 1935, a cautionary tale about dictatorship arising in America. It was seized upon happily by Lewis and anti-Nazi socialists back in those blissful days before the truth about communism was known, i.e. that it was at least as bad as Fascism and operated identically in its oppression of the individual. It might be worth a read, if you can get past the bees that Lewis has in his bonnet about Jews, gays, religion, etc.