I think at the time, the perspective was different. The same era gave us Hogan's Heroes, were almost every German character was played Jewish actors, at least two of which were from Europe. Robert Clary. who played the French POW LeBeau, was in a concentration camp and lost family members at Auschwitz. Of course Roddenberry, Doohan, Kelley and others served in the war. Younger cast and crew were no doubt impacted by the war as well. So many of the people who made TV in the Sixties were "closer" to the subject than we'll ever be. By treating Nazis and their ideology with a serious only, "hands off" attitude we actually give them more power than they deserve.
They were closer than us, yes. Some of them fought the German army on foreign soil, yes. But I think that's still a very different experience from actually having to live under Nazi rule on your own soil, seeing people disappear around you and such. Suppose the U.S would have had to endure all atrocities of Nazi occupation during WW2, would Hollywood in later years have "used" the Nazis slightly differently ?
It's an interesting question perhaps, but not one we'll ever be able to answer.