Oh dear.
Whatever happend to Voltares "I disprove of what you say, but will defend to the death your right to say it"?
EDIT: The irony of this post being downvoted in an attempt to hide it, rather than discuss an opinion you disagree with!
EDIT2: Please understand I have no love for AfD, rather a love of open politics (let everybody hear how crazy they are!).
O tempora, o mores. Back in Voltaire's (sic) days, this would have been an issue between debating gentlemen, not one of massive spreading of hate. It's the fault of media and internet, I know, but that's not so easy to stop.
Anything but address the actual issues that helped catapult them to the top.
The goal posts for those issues will always move.
Look at Japan for instance. For decades, its government's stances on immigration were far to the right of anything in Europe, and guess what, that still didn't stop a far-right faction and its sentiments from taking over.
You can always manufacture anxiety over literally anything, see for instance how the US republican party has made a fight over, like, 10 trans athletes a core pillar of their national culture war.
And regardless, banning a political party (the process for which is set in Germany's constitution) is not the same as banning its former members from speaking.
We have to see this through the lens of modern German history, and the corpus of rules (and lessons from history) that allowed the German Federal Republic to become an independent state again. I think this is not about saying things, but about saying things that foreshadow an attack on the constitution, and then perhaps very likely damaging the institutions of a country in the future.
A democratic state is a suboptimal construct. Once the politcal damaged, it is not easily repaired (See: Some countries East of Germany).
Even if the quote was correct, it is about free speech. Being elected and holding political office is beyond that.