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In the case of Guderian and some others, he initially supported Hitler as he thought could revitalize and save the German nation. Germany was in shambles and being eaten to pieces. There was a period in which a single loaf of bread cost four million to eight million marks. Dollars were the same. People were going down the street with wheelbarrows full of mone, no exaggeration, to buy a single loaf of bread. There are surviving newsreals showing it.
As time went on, Guderian and others became disillusioned and disgusted with Hitler. However, opposition to Hitler in any form whatsoever was lethal, as Rommel found out.
If you read Guderian's autobiography, as the New Yorker reviewer pointed out, "His (Guderian's) contempt for the Nazis is never far from the surface."