On planet X, the group that won during World War II was the Axis power and the ones that took power were called the Nazi party from Germany. Therefore, in this instance, the word "Nazi" is not just added to "make something look worse". Though that does happen a lot and it can be irritating. There is a connect that makes the usage of the word accurate here.
@Chris R Trust me. I saw the episodes with "Planet Nazi", these weren't Nazis. In fact, to even be able to win WWII and have a stable empire, the Nazis would have to change so much that you couldn't call them Nazis anymore.
