Well, in short, the Swastika stands for people that want to end freedom of speech.
The Weimar Republic had complete freedom of speech. But freedom, in all it's forms, also comes with a certain responsebility, something a lot of people tend to forget. And in Germany, this freedom was terribly abused.
So after WW2 Germany learned the lesson that democracy must be able to defend itself. This means that it activly fights everything that wants to challenge the current freedoms. the concept is called "
streitbare Demokratie". Radical parties of the left or right thus were banned, too.
Also, the Swastika is not outrightly banned. In the context of history, in education, historical movies and tv shows it can be used. Just not, for examples for toys, banalaties or as active political symbol. Too many people who became victims of it are still alive. What do you think a Jew wandering the streets of modern Germany suddenly seeing the Swastika again would think?
Also, the Swastika is not just an old Hindu symbol, it also is an old
germanic symbol.
Germany has chosen to go this route, it was not forced on us as some like to state, what other nations do with their own past (including the messsage that delivers) is up to them.