The writers have no fascination with Nazism. Remember that Star Trek came into being only about 20 years after the end of WW2, so the events of that era were still relatively fresh.
The German people take the subject very seriously. They find Nazi jokes to be extremely distasteful. In fact, Nazist references like those depicted in these episodes are banned in Germany.
America has a much greater fascination with WW2 then the rest of the world. (Excluding Japan.)
Germans no doubt can get "bootleg" unedited copies of ST:TOS "Patterns of Force" and ST:ENT "Storm Front" over the internet, from servers located outside of Germany. I am almost certain that at least some German (and Austrian) Star Trek fans know of these episodes, and their content.
Actually ENT: "Storm Front" was aired along with the other episodes in german free TV. And "Patterns of Force" is included and dubbed in german on the DVD´s. The reason why "Patterns of Force" wasn´t aired is, that the ZDF bought Star Trek TOS as a TV show for children in the 70s. You wouldn´t belive what they have done with "Amok Time" in those days, just to make it suitable for children. It is not illegal to deal with Nazi´s in Movies or on TV in Germany and Austria, even in a comic matter like in "Hogan´s Heroes".