If Field Marshall Erwin Rommel did not support the Nazis or Hitler, why did he fight so long and so effectively on he battlefield to defend their government?
He often criticized Hitler in private, and was part of the conspiracy to overthrow him in 1944, so why did he keep fighting instead of just resigning?
I would agree with the above answer, and this was true for many Germans during the war who were never supporters of the Nazis, but were in the war to defend the Fatherland, for better or for worse.
Rommel is a very interesting character, and the essence of the honorable Prussian officer. He treated all prisoners humanely, even Jewish ones, ignoring orders he had been given to kill them upon capture. The Afrika Corps he commanded in North Africa and gained fame for leading as "The Desert Fox" was never accused of war crimes during the fighting there.
Rommel fought so well because he thought it his duty, and because he loved his country. He wanted to exemplify what he thought a German officer should be (as opposed to the example of the Waffen-SS), and later, in 1944 during the bomb plot against Hitler, he wanted to, in his words, rescue Germany.
There were others like him. Karl Doenitz, commander of the Germany Navy and last leader of the Third Reich, and Wilhelm Canaris, head of the German Abwehr, or spy agency were either passively or actively against Hitler while continuing to serve and defend their country.
I would argue that Rommel was not fighting to defend Hitler and the Nazi government. I would argue that he was fighting to defend his homeland. I think that there is a significant difference between these two motivations.
Rommel was known for being a soldier and a patriot. If a person identifies himself in these ways, he is likely to continue fighting no matter what. He will fight as a soldier because he has a responsibility to the men he leads. He will fight as a patriot because he loves his country and does not want to see it destroyed (and, as it turned out, torn in two with part of it handed over to the Soviet Union). These motives will drive a person like Rommel regardless of the nature of the government for which he fights.
Soldiers tend to fight for their comrades and their countries, not for specific governments. This is why Rommel continued to fight so well when he disapproved of Hitler and the Nazis enough to risk (and eventually lose) his life by making his opposition to them known.