I think they think: “Well, in the military/police/security, they break down you down and teach you to just be a mindless drone that just follows orders”. Which is true, but that doesn't mean that gives you the right to go around killing and torturing literally innocent people and children because some general gave you orders. Besides, comparing that to American soldiers during the Vietnam War? How on earth can that make the US look any better?

The Nazis were literally ordered to kill Jews and put them in concentration camps. Many of the SS guards and soldiers were literally volunteers and not conscripted like most American soldiers. Some people inside the Nazi German army deserted to join the Western Allies or the Soviets (either because they were opportunists, communists, liberals or they were conservatives but were against the war or genocide). So the people who were inside the Nazi army were there because they wanted to be there and they knew exactly what they were doing.