|Well, this leads to the ultimate problem, why everyone knows and fears NAZIs, but everyone plays down Communism.|
It's exactly the very problem you described. Nobody knows much about the holocaust and the prisons of old Soviet Russia, but everyone knows about Auschwitz and its horrors, about the German Genozide, about the "Endlösung"-plan of Hitler's dirty little helpers.
My only answer to this is, that probably the horrors of Communism are never to be so evident as the horror of Germany, because Russia has never been invaded by any democratic country. So, there was never as much media coverage about the horrors of Communist Russia, than about NAZI Germany. There movies about Auschwitz, the Schindler-movie and there are the "impressive" performances by Hitler. Stalin wasn't as public about such things to the West and there has never been much coverage about him in the same way as with Hitler.
Those are the fundamental differences that could explain the difference in percetion of Communism and National-Socialism.
The picture of communists that comes to everyones mind, today, is the picture of some drunken/stoned youths sitting in a dirty apartment with a Che Guevara poster at the wall. The picture of National-Socialism, however, is still that of a well-organized group of rude evil-looking statist ready to purge the Earth of anyone opposed to them. The pictures that those words invoke in the general public are very different and those pictures make us feel safer with Communism.
Perhaps everything would be different, if Soviet Russia and the United States had made contact and fought a direct war against each other. Maybe, this would have changed the attitude towards Communism instead of playing it down...
Although Communism was bad, a witch-hunt against alleged Communists is not the answer to anything. If one person amongst those marked on the blackmailing lists was not-guilty, then the whole action becomes obsolete, because you can't sacrifice individuals for a cause that might help, or might not. The danger from the inside was less likely to be dangerous, than the threat from abroad.
If you can't even persuade your own people from believing into your cause, then how can your way be the truth? McCarthy ultimately took a way that involved the premise that Freedom and Liberty were not to be perceived by common men. How else is it justifiable that you had to protect your own people inside the country? What could the Communists possibly have done?
Nothing, which means as much as the US has done within Soviet Russia. Only time showed the Communist population that they didn't like communism. It doesn't matter that McCarthy might have had the best interest, he had no right, nor the moral obligation to act as he did, because he only invoked unreal uneasiness. The same thing that had been evoked after 9/11, the hatred against all Muslimes...